Comparison of 3D-Printed Single Crown Outcomes Among Different Computer-Aided Design Software Programs.

PURPOSE: Low-cost resin 3D printers have been used to produce affordable interim single crowns in public and private dental practices. The purpose of this study was to assess the impact of different computer-aided design (CAD) software programs on 3D trueness, microscopic marginal and internal gaps, time to design, and interproximal contacts of low-cost 3D-printed single crowns. MATERIALS AND METHODS: This in vitro study was performed on a total of 90 standardized resin-prepared teeth adapted to a dental manikin. For comparison among CAD software programs, 45 tooth preparations received 3D-printed crowns designed with one of three CAD software programs by an experienced technician and identified as groups TRIOS (n = 15), EXOCAD (n = 15), and ZZ (Zirkonzahn; n = 15). To assess interoperator reproducibility, 15 additional crowns were designed by a dental clinician (group ZZ-DENT) and 15 by a dental prosthetic technician (group ZZ-PROS), both with basic 1-week CAD/CAM training. Finally, as a control group, 15 crowns were milled using a high-end five-axis milling device (group ZZ-CONTROL). Statistically significant differences for 3D trueness, microscopic gaps, time to design, and interproximal contacts among groups were assessed with the Kruskal-Wallis test. RESULTS: No statistically significant differences in 3D trueness or marginal or internal gaps were found, either among different software programs or CAD operators (P > .05). However, Group TRIOS took significantly longer to design than EXOCAD and ZZ groups (P = .001). Less-experienced operators were significantly outperformed in time and interproximal contacts (P = .001) by the CAD technician using the same software program. Finally, control milled crowns (ZZ-CONTROL) significantly outperformed the respective 3D-printed copies (ZZ) in all assessed variables (P < .001). CONCLUSIONS: Different CAD software programs may affect the time required to design, but they do not significantly affect clinical outcomes of low-cost 3D-printed resin crowns if designed by an experienced CAD technician.

Does Clinical Experience Affect Chairside Digital Waxing of Single Crowns More Than Software Training?

PURPOSE: To compare the accuracy of dentists with different levels of expertise in computer-aided design (CAD) and prosthodontics to digitally design single crowns. MATERIAL AND METHODS: This in vitro study was conducted on 12 prepared teeth in 2 reference dental study models. The models were scanned using an intraoral scanner. Four dentists with different levels of clinical and CAD expertise (PROS: clinicians experienced in prosthodontics [n = 2]; CAD: experts in CAD [n = 2]) performed digital waxing on all prepared teeth using the same CAD software program. The resulting digital crown designs were compared to STL files of the original teeth to assess 3D deviations. The total cervical, distal, mesial, and occlusal surface deviations of the crowns from both groups were compared using paired t and Wilcoxon signed-rank tests (α = .05). RESULTS: The total median 3D deviation was 0.10 mm (range: 0.03 to 0.61 mm) for the PROS group and 0.14 mm (range: 0.07 to 0.58 mm) for the CAD group. The PROS group presented significantly smaller total 3D (P = .021) and cervical margin (P = .001) deviations. There were no significant differences between groups on the distal, mesial, or occlusal surfaces (P > .05). The CAD group performed digital waxing significantly faster (P = .001). CONCLUSION: Within the limitations of this study, the present findings suggest that clinical experience has a higher impact on the accuracy of digital wax patterns of single crowns than CAD experience.

Computer-aided design expertise affects digital wax patterns of CAD/CAM laminate veneers more than single crowns.

AIM: There is controversy in the literature regarding clinical outcomes of CAD/CAM laminate veneers. The aim of the present study was to assess the impact of different levels of CAD expertise and different software programs on the reliability and reproducibility of digital wax patterns of laminate veneers and single crowns. MATERIALS AND METHODS: The present preliminary in vitro study was performed on 10 prepared maxillary central incisors available in dental study models. Of the total, five central incisors were prepared with shoulder finish lines for single crowns, whereas the other five underwent incisal shoulder preparation for laminate veneers. The models were scanned using an intraoral scanner. Four dentists (group DENT) and four CAD dental technicians (group CAD) with expertise in different software programs performed digital diagnostic waxing on all prepared teeth. The resulting digital wax patterns (n = 80) were exported as standard tessellation language (STL) files and superimposed on gold standard digital wax patterns (obtained from the original shape of the teeth before preparations). 3D mesh deviations at the cervical margins as well as distal, mesial, and incisal/palatal surfaces between each STL and the gold standard digital wax patterns were calculated in millimeters using a CAD software program. The mean time required by each operator to perform digital waxing was also recorded. Paired comparisons between groups DENT and CAD as well as between nondental and dental software programs were performed for the crowns and laminate veneers using the Wilcoxon signed-rank and paired t tests (α = 0.05). RESULTS: For group DENT, median deviations for single crowns were 0.15 mm (range: 0.08 to 1.05 mm) and for laminate veneers they were 0.15 mm (range: 0.08 to 0.76 mm). For group CAD, median deviations for single crowns were 0.16 mm (range: 0.09 to 0.73 mm) and for laminate veneers they were 0.10 mm (range: 0.06 to 0.53 mm). The Wilcoxon signed-rank test revealed a statistically significant difference between groups DENT and CAD (P = 0.041) and between the software programs (P = 0.029) for laminate veneers, but not for single crowns (P > 0.05). Furthermore, mean times required for group CAD and for dental software programs were significantly shorter than those for group DENT (P = 0.001) and for nondental software programs (P = 0.001), respectively. CONCLUSION: Within the limitations of the present study, the findings suggest that CAD expertise and the software program significantly affect digital wax patterns for laminate veneers, but not for single crowns. (Int J Comput Dent 2022;25(4):361-0; doi: 10.3290/j.ijcd.b3555819).

Effect Of Different Milling Devices On Marginal Fit Of CAD-CAM Zirconia Copings On Implant Stock Abutments.

PURPOSE: To compare the marginal fit and internal surface roughness of CAD/CAM zirconia copings milled with 3- and 5-axis milling devices. MATERIALS AND METHODS: Forty titanium implant stock abutments (4.8 mm in diameter, 4 mm in height) screwed to dental implants (4.1 mm in diameter) embedded in resin were considered phantoms and included in this in vitro study. All 40 phantoms were scanned with the same intraoral scanner, from which images of the virtual wax-up of zirconia copings were obtained and exported as standard tessellation language (STL) files. From each resulting STL file, two copings were milled: one using a 3-axis milling device, and the other using a 5-axis milling device. After milling, zirconia copings underwent high-speed sintering before being analyzed for marginal fit (ie, marginal gap measurement), and internal surface roughness was assessed with a scanning electron microscope (SEM). Statistical comparisons between groups were assessed with Mann-Whitney test. RESULTS: Median marginal gap values were 34.80 µm (95% CI: 0.00 to 173.98) for the 5-axis milling device group and 141.97 µm (95% CI: 82.13 to 163.46) for the 3-axis milling device group. A statistically significant difference in marginal gap was found between both milling device groups (P = .039). In addition, qualitative SEM analysis indicated higher internal surface roughness for the 3-axis milling device group. CONCLUSION: Within the limitations of this study, the present findings suggest that 5-axis milling devices outperform 3-axis milling devices for milling CAD/CAM zirconia copings from intraoral scans of implant stock abutments.

Effect of varying levels of expertise on the reliability and reproducibility of the digital waxing of single crowns: A preliminary in vitro study.

STATEMENT OF PROBLEM: The digital waxing of single crowns can be affected by the quality of intraoral scans and use of computer-aided design (CAD) software programs. However, clinical outcomes of the resulting crowns are also affected by computer-aided manufacturing (CAM) methodologies. Studies on the effect of different levels of expertise on digital waxing are lacking. PURPOSE: The purpose of this in vitro study was to assess the impact of different levels of expertise on the reliability and reproducibility of margin outlining during digital waxing. MATERIAL AND METHODS: Thirty analogs of implant stock abutments (Ø4.8×4 mm) were embedded into resin blocks. To simulate different clinical situations, abutments were divided into 3 groups: 10 abutments (group GOS) received artificial gingiva and were scanned with an open system intraoral scanner, while 10 abutments with (group GIS) and 10 abutments without artificial gingiva (group IS) were scanned with an intraoral scanner within an integrated CAD-CAM system. All resulting standard tessellation language (STL) files were used by 2 different observers (an experienced CAD professional and a clinician with basic CAD knowledge) to digitally design a left mandibular central incisor in the same software program. All resulting digital crown designs were exported to STL files to assess crown margin accuracy at the coupling interface by superimposition with the control STL file of the scan body designed for the same abutment by the manufacturer. For this purpose, a CAD software program was used to automatically calculate median, minimum, and maximum deviations of margins in millimeters. Statistically significant pairwise differences among groups and between observers were assessed with the Wilcoxon signed-rank test (α=.05). RESULTS: For the CAD professional, median deviations between designed crown STL files and the control STL of the scan body were 0.08 mm (range: 0.04 to 0.15) for group GOS; 0.10 mm (range: 0.06 to 0.18) for group GIS; and 0.05 mm (range: 0.03 to 0.08) for group IS. For the clinician, median deviations were 0.08 mm (range: 0.04 to 0.12) for group GOS; 0.11 mm (range: 0.07 to 0.17) for group GIS; and 0.05 mm (range: 0.04 to 0.11) for group IS. There were no significant differences between observers (P>.05). However, statistically significant differences were found between group IS and the other 2 groups (P=.001) but not between groups GOS and GIS (P>.05). CONCLUSIONS: The present findings suggest that a digital wax pattern made with a dental CAD software program is not affected by varying levels of expertise but might be affected by subgingival margins.

Clinical relevance of Digital Dentistry during COVID-19 outbreak: a scoped review

Aim: To perform a scoped literature review on advantages of digital workflows in dentistry that could be widely adopted to address safety issues raised during the coronavirus (COVID-19) pandemic. Methods: Recent studies on any advantages of digital dentistry ­ as compared to conventional methods ­ that could help addressing the new safety demands for dental treatments that emerged due to the current pandemic were included. PUBMED, Embase, and Web of Knowledge databases were searched for eligible articles published in the last five years. The guidelines of PRISMA statement were followed during data extraction and evaluation. Results: The present search strategy yielded 181 publications. After application of exclusion criteria, a total of 34 studies were finally considered eligible to be discussed. Among the most important advantages of digital dentistry that contribute to safety during the current pandemic are: reduced number of clinical appointments required, shorter chairside time, less invasive surgeries and safer procedures. Conclusion: Within the limitations of this study, the findings observed herein suggest that the use of digital workflows in dentistry could lead to increased safety and reduced transmission of COVID-19 during the current pandemic

Scanning Electron Microscopy Analysis of the Adaptation of Single-Unit Screw-Retained Computer-Aided Design/Computer-Aided Manufacture Abutments After Mechanical Cycling.

PURPOSE: To measure the microgap between dental implants and custom abutments fabricated using different computer-aided design/computer-aided manufacture (CAD/CAM) methods before and after mechanical cycling. MATERIALS AND METHODS: CAD software (Dental System, 3Shape) was used to design a custom abutment for a single-unit, screw-retained crown compatible with a 4.1-mm external hexagon dental implant. The resulting stereolithography file was sent for manufacturing using four CAD/CAM methods (n = 40): milling and sintering of zirconium dioxide (ZO group), cobalt-chromium (Co-Cr) sintered via selective laser melting (SLM group), fully sintered machined Co-Cr alloy (MM group), and machined and sintered agglutinated Co-Cr alloy powder (AM group). Prefabricated titanium abutments (TI group) were used as controls. Each abutment was placed on a dental implant measuring 4.1× 11 mm (SA411, SIN) inserted into an aluminum block. Measurements were taken using scanning electron microscopy (SEM) (×4,000) on four regions of the implant-abutment interface (IAI) and at a relative distance of 90 degrees from each other. The specimens were mechanically aged (1 million cycles, 2 Hz, 100 N, 37°C) and the IAI width was measured again using the same approach. Data were analyzed using two-way analysis of variance, followed by the Tukey test. RESULTS: After mechanical cycling, the best adaptation results were obtained from the TI (2.29 ± 1.13 µm), AM (3.58 ± 1.80 µm), and MM (1.89 ± 0.98 µm) groups. A significantly worse adaptation outcome was observed for the SLM (18.40 ± 20.78 µm) and ZO (10.42 ± 0.80 µm) groups. Mechanical cycling had a marked effect only on the AM specimens, which significantly increased the microgap at the IAI. CONCLUSION: Custom abutments fabricated using fully sintered machined Co-Cr alloy and machined and sintered agglutinated Co-Cr alloy powder demonstrated the best adaptation results at the IAI, similar to those obtained with commercial prefabricated titanium abutments after mechanical cycling. The adaptation of custom abutments made by means of SLM or milling and sintering of zirconium dioxide were worse both before and after mechanical cycling.

Avaliação da adaptação marginal de pilares unitários em zircônia personalizados por sistema CAD/CAM: estudo laboratorial / Margin fit of single, customized zirconia CAD/CAM implant abutments: in vitro study

O uso de pilares e infraestruturas cerâmicas pelo método CAD/CAM tem se popularizado nas reabilitações, seja para implantes ou dentes naturais. O objetivo deste estudo foi avaliar a adaptação de um pilar de hexágono externo obtido em zircônia através do processo CAD/CAM. Para tanto, foram confeccionados dez pilares em zircônia (grupo teste) de um mesmo arquivo obtido através do escaneamento de um análogo de implante HE 4,1. Foram utilizados dez pilares em titânio da mesma empresa que produziu o análogo (grupo controle). Cada amostra foi instalada no análogo com torque de 32 Ncm, sendo levadas a microscopia óptica, onde foram medidos três pontos para cada amostra. Os resultados demonstraram média de desadaptação de 3,88 µm no grupo teste e 4,36 µm no grupo controle, ficando ambas abaixo do limite preconizado pela literatura. Este trabalho permitiu concluir que é possível conseguir adaptação satisfatória com pilares unitários em zircônia obtidos pelo método CAD/CAM.

The use of ceramic frameworks and abutments has become popular in tooth- or implant-supported oral rehabilitations. The aim of this study was to evaluate the margin fit of a CAD/CAM generated, external hex zirconia abutment. For this, ten zirconia abutments (test group) were obtained from scanning of a 4.1mm implant replica. Ten titanium abutments served as control. Each sample was tightened to 32 Ncm and three regions observed under light microscopy. The mean margin fit levels were 3,88 micrometers and 4.36 mm in the control group, being those values lower than that reported in the literature. It can be concluded that satisfactory fit can be found on CAD/CAM single, zirconia abutments

Stress distribution after installation of fixed frameworks with marginal gaps over angled and parallel implants: a photoelastic analysis.

PURPOSE: The objective of this work was to compare by photoelastic analysis the stress distribution along a fixed framework placed over angled or parallel implants with different gap values between the framework and one of the implants. MATERIALS AND METHODS: Two photoelastic models were created: (i) with parallel implants; (ii) with a 30 degrees angled central implant. In both cases, three implants were used, and CP titanium frameworks were constructed with commercial components. A plane polariscope was used to observe the photoelastic fringes generated after initial framework assembly, and also when an axial load of 100 N was applied over the central implant. For both models, stress analysis was conducted on well-fitting frameworks and on another with a 150 microm vertical gap between the framework and the central implant. RESULTS: The photoelastic analysis indicated that in the model with parallel implants, stress distribution followed the implant axis, and in the model with an angled implant, a higher and nonhomogeneous stress concentration was observed around the apical region of the lateral implants. The placement of an ill-fitting framework resulted in increased preload stress patterns. CONCLUSION: Stresses were generated after screw tightening of the frameworks, increasing when a load was applied and when a vertical gap was present. Angled implants resulted in oblique stress patterns, which were not transferred with homogeneity to the polymeric model.

Avaliação da aplicabilidade da análise de Carrea na dentadura decídua / Evaluation of the applicability of the Carrea analisys on the primary dentition

A procura por manobras preventivas tem levado o Odontopediatra e o Clínico Geral a conhecerem melhor os padrões de crescimento e desenvolvimento dos arcos dentais decídos. Com esse intuito, foram examinados 60 modelos de arcadas dentárias de crianças leucodermas das escolas primárias do município Melena Del Sur, na província de Havana, Cuba. A amostra foi dividida em quatro grupos, de acordo com a faixa etária, dos 5 aos 6 anos e 6 meses, por sexo e pelo tipo de arco segundo Baume. A essa amostra foi aplicada a análise de Carrea, na qual a oclusão das crianças selecionadas seguiu o padrão de normalidade. Observaram-se diferenças significantes entre a forma dos arcos dentários em crianças durante o desenvolvimento da oclusão, determinado pelo sexo e o tipo de arco segundo Baume. O método de Carrea aplicado à amostra obteve correspondência nas medidas sempre acima de 60%. Concluiu-se que o método de Carrea pode ser utilizado para o diagnóstico oclusal e ortodôntico/ortopédico-facial, entretanto seus resultados devem ser considerados com cautela.

Photoelastic analysis of stress distribution on parallel and angled implants after installation of fixed prostheses.

The longevity of implant-supported prosthetic rehabilitation depends largely on how the masticatory forces are transferred to the implants and surrounding bone. Anatomical conditions, bone morphology and aesthetics usually dictate implant placement in less than ideal positions for prosthetic rehabilitation and sometimes it is possible to find them with different inclinations. The purpose of this paper was to compare, through photoelastic analysis, the stress distribution in a fixed prosthesis with 3 parallel implants, to the stress distribution in the same prosthesis in the existence of an angled central implant. Two photoelastic resin models were made and a polariscope was used in the visualization of isochromatic fringes formed in the models when axial loads of 2 kg, 5 kg and 10 kg were applied to a unique central point of the prosthesis. The presence of inducted tensions (preloads) was observed in the models after applying torque to the retention screws. Preloads were intensified with the incidence of occlusal forces. In the parallel implants, the force dissipation followed the long axis. The angled implant had a smaller quantity of fringes and the stresses were located mostly around the apical region of the lateral implants.

Photoelastic analysis of stress distribution on parallel and angled implants after installation of fixed prostheses

A longevidade das reabilitações orais implanto-suportadas depende, em grande parte, de como as forças mastigatórias são transferidas aos implantes e ao osso que os circunda. Condições anatômicas, morfologia óssea e estética muitas vezes ditam a colocação de implantes em posições que não são ideais para a reabilitação protética, e podemos encontrá-los com diferentes inclinações. A proposta deste trabalho foi comparar, através de análise fotoelástica, a dissipação de tensões em uma prótese fixa com 3 implantes paralelos entre si com a dissipação de tensões na mesma prótese na existência do implante central angulado. Foram confeccionados dois modelos de resina fotoelástica. Utilizou-se um polariscópio para visualização das franjas isocromáticas que se formaram nos modelos fotoelásticos quando cargas axiais de 2 kg, 5 kg e 10 kg foram aplicadas em um mesmo ponto central da prótese. Verificou-se a indução de tensões (pré-tensões) nos modelos após o apertamento dos parafusos de retenção das próteses. As pré-tensões foram agravadas com a incidência de forças oclusais. Nos implantes paralelos, a dissipação de forças seguiu os longos eixos. No implante angulado houve menor quantidade de franjas, e as tensões estavam localizadas principalmente ao redor da região apical dos implantes laterais.

Alteraçäo dimensional de amálgama de prata e liga à base de gálio / Dimensional alteration of silver amalgam and gallium-based alloy

As ligas de gálio surgiram como alternativa à problemática da toxicidade do mercúrio. Apresentam propriedades semelhantes às do amálgama, mas as pesquisas apontam duas características desfavoráveis: corrosäo excessiva e grande magnitude de expansäo de presa, podendo causar fraturas e rachaduras nas extruturas dentais. O objetivo foi avaliar in vitro a alteraçäo dimensional durante 7 dias de uma liga de gálio (Galloy, SDI, Austrália), comparativamente com uma liga de amálgama contendo zinco (F-400, SDI, Austrália), em funçäo do contato e/ou contaminaçäo com soluçäo salina (NaCl 0,9 por cento) nos estágios iniciais da cristalizaçäo. As condiçöes experimentais de armazenagem foram em : ambiente seco; armazenagem em soluçäo salina durante a condensaçäo. Para o amálgama, foi ainda estudada a condiçäo de contaminaçäo introduzida na cápsula durante a trituraçäo e para a liga de gálio, a proteçäo com resina fluida durante as primeiras 24h ou durante todo o experimento. Os corpos-de-prova foram mantidos à temperatura de 37ºC ñ 1ºC e suas dimensöes monitoradas a cada 24h, durante sete dias. O contato da liga de gálio com a soluçäo salina durante a condensaçäo ou nas primeiras horas após a condensaçäo desencadeou uma expansäo significantemente maior que as outras condiçöes experimentais ao fim dos 7 dias. A aplicaçäo de uma resina fluida para proteger a superfície dos cilindros foi capaz de evitar o aumento da expansäo provocado pela umidade superficial. O amálgama näo apresentou alteraçöes significantes em nenhuma das condiçöes experimentais, exceto quando contaminado durante a trituraçäo