Effect of different implant locations and abutment types on stress and strain distribution under non-axial loading: A 3-dimensional finite element analysis.

Background/purpose: Dental implants have been a popular treatment for replacing missing teeth. The purpose of this study was to investigate the impact of engaging (hexagonal) and non-engaging (non-hexagonal) abutments in various six-unit fixed prosthesis on the stress distribution and loading located in the implant neck, implant abutment, and surrounding bone. Materials and methods: Three implants were digitally designed and inserted parallel to each other in edentulous sites of the maxillary right canine, maxillary right central incisor, and maxillary left canine. Titanium base engaging abutments, non-engaging abutments and connecting screws were designed. Five distinct models of 6-unit fixed dental prosthesis were created, each featuring different combinations of various abutments. Forces (45-degree angle) were applied to the prosthesis, allowing for the analysis of the stress distribution on the implant neck and abutments, and the maximum and minimum principal stress values on the cortical and trabecular bone. Results: Von Mises stress values and stress distributions located in the implant neck region due to the applied loading forces were analyzed. The overall stress values were highest while employing the hexagonal abutments. The maxillary left canine with a hexagonal abutment (model 5) reported the highest von mises value (64.71 MPa) while the maxillary right canine with a non-hexagonal abutment (model 4) presented lowest von mises value (56.69 MPa). Conclusion: The results suggest that both the various abutment combinations (engaging and non-engaging) on five different models have a similar influence on the distribution of stress within the implant system.

Influence of the implant scan body modifications on trueness of digital impressions.

Background/purpose: Effects of implant angulation on digital impression accuracy remain controversial. The purpose of this study was to assess the relationship between the alteration of implant scan bodies and the trueness of digital impressions. Materials and methods: A maxillary typodont without the right premolars and first molar was scanned with a laboratory scanner and saved as a standard triangular language (STL) file. A model from the STL file was fabricated with a 3-dimensional printer. Two implants were placed into the first premolar and first molar sites of the model, followed by the insertion of two scan bodies onto the implants. These scan bodies were divided into four test groups, based on the surface modifications. A digital impression of each typodont was made with three different intraoral scanners. An abutment was digitally seated on each implant. 120 STL files (30 for each group) of the typodont with two implants and two corresponding abutments were used for statistical analysis. Results: A total of 240 values (two implants for each typodont) were obtained after each sample (4 groups) was scanned 10 times by utilizing three intraoral scanners. The overall linear and angular discrepancies were analyzed. Group 1 showed the lowest linear discrepancy of 14.9 ± 5.4 µm while Group 4 reported the highest linear discrepancy of 137.5 ± 41.7 µm, yielding a statistical significance (P < 0.05). Conclusion: It has been concluded that the more adjustments made to the scan bodies, the greater the linear and angular deviations occur, compromising the trueness of the digital implant impression.

A Randomized Clinical Trial of Monolithic Single-Tooth Crowns: 1-Year Preliminary Results.

PURPOSE: To investigate the clinical results of single-tooth ceramic crowns in the posterior region produced from three different monolithic materials. MATERIALS AND METHODS: A total of 36 posterior single-tooth crowns were fabricated from lithium silicate glass-ceramic (LSGC; n = 12), lithium disilicate glass-ceramic (LDGC; n = 12), and polymer-infiltrated ceramic network (PICN; n = 12) in 27 patients. Restorations were evaluated for prosthetic and periodontal criteria at baseline (0) and after 6 and 12 months. Prosthetic evaluation was performed according to the modified United States Public Health Service (USPHS) criteria, and probing depth (PD), clinical attachment level (CAL), gingival bleeding time index (GBTI), and gingival (GI) and periodontal indices (PI) were evaluated in the periodontal assessment. Friedman and Kruskal-Wallis tests were used for statistical analyses (P = .05). RESULTS: All restorations were evaluated according to survival and success rates. No dropouts occurred. The survival rate of all three materials was 100% after 1 year. However, in the PICN group, a statistically significant difference was found between baseline and 12 months for color match (from A to B) and surface texture (from A to C; P < .001). CONCLUSIONS: Although long-term clinical follow-up periods are needed, all three ceramics showed clinically acceptable survival and success rates over 1 year. The ceramics evaluated in the present study could be preferred for single-tooth full-crown restorations in the posterior region.

Fit of High-Translucency Zirconia Fixed Dental Prostheses Using Two Different Intraoral Scanners.

PURPOSE: To assess the marginal and internal fit of monolithic zirconia fixed dental prostheses (FDPs) comparing two different intraoral scanners (IOSs) and assessment methods. MATERIALS AND METHODS: A maxillary typodont with three prepared teeth allowed fabrication of five-unit high-translucency monolithic zirconia FDPs. The typodont was scanned with two IOSs: Cerec Omnicam and 3Shape TRIOS 3. In total, 30 FDPs were milled from presintered high-translucency zirconia blocks. Dual-scan and silicone replica assessments were used to determine marginal and internal gaps. RESULTS: A statistical significance was observed for marginal gaps (3Shape [74.27 ± 10.4 µm] and Cerec [86.45 ± 14.3 µm]) and for internal gaps (3Shape [126.12 ± 12.7 µm] and Cerec [112.38 ± 17.2 µm]). CONCLUSIONS: The outcomes of this study showed that the 3Shape TRIOS 3 produced a better overall marginal fit, while the Cerec Omnicam created a better internal fit. Additionally, a greater overall marginal and internal gap was noted with the silicone replica method over the dual-scan method.

Analysis of the impact of various finish line designs and occlusal morphologies on the accuracy of digital impressions.

Background/purpose: Recent advancements in dental technology has led clinicians to convert from traditional methods to digital workflows. The purpose of this study was to analyze the effect of various finish line designs and occlusal morphologies on the accuracy of digital impressions. Materials and methods: Six maxillary molar crown preparations were designed by using a digital sculpting software program. The samples differed in finish line design and occlusal surface morphology. Three different finish line designs (shoulder, chamfer, and shoulder with internal round angle) and two different occlusal morphologies (sharp and rounded) were used, giving six groups. Using three different intraoral scanners, each group was scanned and compared with a reference scan obtained from an industrial scanner. The accuracy of each scan was studied, and the data were statistically analyzed. Results: A total of 180 scans were acquired by utilizing three different intraoral scanners. The reference scan was compared with the scans from each group and overall differences (marginal, axial, and occlusal) were assessed. A crown preparation with a chamfer finish line showed the lowest marginal discrepancy of 13.2 ± 4.18 µm while preparation with a shoulder finish line reported the highest discrepancy of 34.8 ± 7.9 µm (P < 0.05). Also, the occlusal discrepancies of the samples with rounded and sharp occlusal morphologies were 12.55 ± 3.09 µm and 19.13 ± 2.3 µm, respectively (P < 0.05). Conclusion: It has been suggested that chamfer finish line design and rounded occlusal anatomy may produce more accurate digital impression for single crown restorations.

Accuracy of digital impressions for implant-supported complete-arch prosthesis when using an auxiliary geometry device.

Background/purpose: Digital impressions using intraoral scanners have recently gained popularity. The aim of the present study was to evaluate the fit of full-arch screw-retained cobalt-chromium frameworks fabricated via two different digital impression methods. Materials and methods: An edentulous resin master model with four dental implants was fabricated. Forty cobalt-chromium superstructures were fabricated and evaluated according to four groups. In Group 1, the superstructures were evaluated using an intraoral scanner to generate digital impressions. Group 2 relied on the help of an auxiliary geometric appliance in generation of digital impressions via intraoral scanner. The traditional method of splinted open-tray conventional impressions was designated for Group 3. Finally, the control group (Group 4) relied on scanning of the master model directly with a laboratory scanner. Vertical marginal discrepancy was evaluated, and data obtained were statistically analyzed. Results: The highest mean vertical marginal gap value (80.86 ± 50.06 µm) was observed for Group 1 and statistically higher than Group 2, 3, and 4 (P < 0.05). The lowest mean vertical marginal gap value (41.98 ± 26.33 µm) was measured from Group 4 and statistically similar to Group 2 and 3 (P > 0.05). Conclusion: It has been suggested that the use of auxiliary geometric appliances yields increased scanning accuracy. Frameworks fabricated using the traditional splinted open-tray technique were more reliable compared to those frameworks from digital impressions.

Performance of high-translucent zirconia CAD/CAM fixed dental prostheses using a digital workflow: A clinical study up to 6 years.

Background/purpose: Zirconia has recently become a popular material for fixed restorations. The purpose of this study was to use a digital workflow to fabricate monolithic zirconia fixed dental prostheses (FDPs) and assess the connection between variable connector sizes compared to their clinical performance. Materials and methods: Clinicians evaluated monolithic zirconia FDPs in 58 patients. After definitive impressions were made, stone casts were obtained. The stone casts were scanned to a standard triangle language (STL) file. A digital wax up was fabricated, and corresponding provisional restorations were milled. Final FDPs were fabricated from a high-translucent zirconia material. During digital fabrication, the connector area of each FDP was recorded while meticulous attention was paid to ensure that the connector cross-sectional area was ≥9 mm2 for the 3-unit restorations (pontic to retainer) and ≥12 mm2 for the 4-unit restorations (pontic to pontic). Biological an technical outcomes of the FDPs were performed at 1 week, 6 months and then annually for 6 consecutive years. Results: A total of 23 men and 35 women received a total of 63 full-contour zirconia FDPs in the posterior regions and were observed for a time period ranging between 50 and 70 months. No decementation occurred and no caries were detected during the observation period, however signs of gingivitis were detected in 4 patients. The dimension of the connector areas was 12 mm2 in the two broken 4-unit FDPs. Conclusion: The results of this study suggest that the use of digital scanning and milling to fabricate monolithic zirconia FDPs of posterior regions may be an acceptable alternative restorative approach to traditional metal-ceramic restorations.

Effect of sintering time on the marginal and internal fit of monolithic zirconia crowns containing 3-4 mol% Y2O3.

BACKGROUND: Short-term sintering may offer advantages including saving time and energy but there is limited evidence on the effect that altering sintering time has on the accuracy of monolithic zirconia crowns. The purpose of this in vitro study was to investigate the effect of shortened sintering time on the marginal and internal fit of 3Y-TZP and 4Y-TZP monolithic crowns. METHODS: Sixty monolithic zirconia crowns were fabricated for the maxillary first molar tooth on the prefabricated implant abutment. Groups were created according to the material composition: 3Y-TZP Generation 1, 3Y-TZP Generation 2 and 4Y-TZP. Two different sintering protocols were performed: same final sintering temperature (1500 °C) and various rates of heating (10 °C/min and 40 °C/min), cooling down speed (- 10 °C/min and - 40 °C/min), holding time (45 and 120 minutes), and total sintering time (approximately 2 and 7 hours, respectively). The marginal and internal fit of the crowns were determined using the silicone replica technique. Comparisons between groups were analyzed using two-way ANOVA. Pairwise multiple comparisons were performed using t-test (p < 0.05). RESULTS: The mean marginal gap values of 4Y-TZP zirconia revealed statistically significant increase for the short-term sintering protocol (p < 0.0001), while no difference was observed between the sintering protocols for the mean marginal gap values of 3Y-TZP groups. Although all groups showed clinically acceptable gap values, altering the sintering time had an effect on marginal fit of the crowns manufactured from 4Y-TZP zirconia. CONCLUSIONS: Shortening the sintering time may lead to differences within clinically acceptable limits. The manufacturer's recommendations according to material composition should be implemented with care.

Future expectations, career choices and related factors among dental students: A cross-sectional study.

Purpose: The aim of this study was to determine descriptive characteristics of dental students, to investigate their professional expectations, career decision criteria, and related factors; to examine how (if any) seniority in school affects these. Subjects and methods: During the period of 2018-2019, all 1-5 grade students (n = 754) of Hacettepe University Dental School were invited to participate and those who accepted had filled under observation a standard questionnaire form of 35 questions (83.4%). In the analysis of the data, descriptive statistics, chi-square, Student's t-test and ANOVA and Odds ratio methods were used. Results: In this cross-sectional study, 66% of the group were female, age range was 18-30 (mean±SD= 21.2 ± 1.7). The most common reasons for choosing dentistry were "financial benefits", "job security" and "professional status". "Undertake specialist training" (80.2%) was the most common short-term expectation after graduation; two most common long-term expectations were "having a private clinic" (57.9%) and "completing specialization training" (56.0%). The most important factors affecting the post-graduation working plans were work-life balance and economic stability. Conclusion: It is recommended to provide adequate counseling and guidance to students about potential career paths to maximize a balanced and widely accessible oral health service delivery across the country with more motivated dentists. Qualitative research may improve our understanding of how dental education can be improved to fulfill students' expectations from school, and to motivate dental students towards general practitioning in the future.

Clinical, Technical, and Radiologic Outcomes of 182 Implant-Supported Zirconia Single Crowns Using Titanium-Base Abutments: A Retrospective Study.

PURPOSE: To evaluate the biologic, technical, and radiographic outcomes of CAD/CAM-milled bilayer and monolithic zirconia crowns using implants and Ti-base abutments with up to 5 years of follow-up. MATERIALS AND METHODS: A total of 182 implant-supported "screw-mentable" (hybrid screw/cement retention) single crowns were evaluated in 118 patients. Ti-base abutments were selected according to the chimney (3.5 or 5 mm) and gingival (1, 2, or 3 mm) heights in the virtual model. Zirconia crowns were designed using CAD/CAM software and then milled from partially stabilized zirconia blocks. After all crowns were cemented onto Ti-base abutments, they were clinically screwed onto the implants. Both implants and crowns were followed up for up to 5 years, and their clinical, technical, and radiologic results were recorded. RESULTS: A total of 118 patients (86 women and 32 men) who received 182 implant-supported screw-mentable crowns were included in this study. The mean follow-up period was 32 ± 18 months (range: 24 to 60 months) for all implants and crowns. No implant was lost during the follow-up period, yielding a cumulative implant survival rate of 100%. Two technical complications were observed in two bruxer patients, yielding a cumulative restoration survival rate of 98.9%. The marginal bone loss was 0.7 ± 0.5 mm from the baseline radiograph to the radiograph taken at the final recall visit. No implants were diagnosed with peri-implantitis. CONCLUSION: The outcomes of this study suggest that Ti-base abutments are a feasible and affordable alternative to CAD/CAM abutments and that they can successfully support single zirconia crowns.

Comparison of marginal and internal fit of 5-unit zirconia fixed dental prostheses fabricated with CAD/CAM technology using direct and indirect digital scans.

BACKGROUND/PURPOSE: Advancements in digital dentistry and the development of intraoral scanners (IOS) have provided clinicians with an accurate and efficient alternative to analog impressions. The aim of this study was to assess the accuracy of the marginal and internal fit of 5-unit monolithic zirconia fixed dental prostheses (FDPs) fabricated with CAD/CAM technology using direct and indirect digitalization methods. MATERIAL AND METHODS: Three teeth in a maxillary typodont model were prepared to receive a 5-unit zirconia FDP. Six different groups were created according to the type of scanner (intraoral and extraoral) and the type of workflow. For direct workflow, the typodont was scanned with two different IOS (3Shape Trios 3 [3S-IOS] and Cerec Omnicam [C-IOS]). For indirect workflow, after conventional impressions were obtained, the impressions (IMP) were scanned with two different laboratory scanners (3S-IMP and C-IMP). After the impressions were poured, the stone (STN) casts were scanned with the same laboratory scanners (3S-STN and C-STN). Sixty 5-unit monolithic zirconia FDPs (10 in each group) were designed and milled. The marginal and internal fit was assessed. RESULTS: The mean marginal gap values were 78.2±9 µm in the IOS group, 82.6± 9 µm in the IMP group, and 82.6±9 µm in the STN group, indicating no statistically significant differences among groups (p > 0.05). The mean axial gap values were 77.7 ± 10 µm in IOS group, 83.61 ± 15 µm in the IMP group, and 84.5±9 µm in the STN group, indicating no statistically significant differences among groups (p > 0.05). CONCLUSION: The marginal and internal fit of 5-unit monolithic zirconia FDPs fabricated with direct and indirect digital scans were similar. The smallest gap values were observed at the marginal region while the greatest gap values were detected at the occlusal region.

Effect of Anti-Rotational Abutment Features and Novel Computerized Fabrication Techniques on the Marginal Fit of Implant-Supported Metal Copings.

PURPOSE: An in vitro study to compare the marginal fit of cobalt-chromium (Co-Cr) metal copings fabricated with selective laser melting (SLM), computer-aided design and computer-aided manufacturing (CAD/CAM) milling, and lost-wax (LW) techniques, on abutments with two different antirotational features. MATERIALS AND METHODS: A total of 60 stainless steel abutments with the same length and convergence angles were fabricated using a numerical control machining. Half of the abutments had one flat plane, while the other half had three grooves as an antirotation feature. Thirty abutments of each kind were then divided into three subgroups, and metal copings were fabricated with SLM, CAD/CAM milling, or the LW technique (n = 10). The metal copings were cemented with polycarboxylate cement. Marginal gap measurements were performed using a stereomicroscope at a magnification of × 45 and data were analyzed with two-way analysis of variance (ANOVA) tests. RESULTS: The LW (p = 0.002) and CAD/CAM (p < 0.001) techniques exhibited increased marginal gaps on the abutments with a three groove antirotational feature; however, no significant difference was detected with the SLM technique (p = 0.259). The copings fabricated with the SLM technique demonstrated significantly lower gap values in both abutment types (p < 0.001). CONCLUSION: While all marginal gap values were within the clinically acceptable range (<120 µm), abutments with more antirotational grooves exhibited wider marginal gaps with the LW and CAD/CAM techniques.

Comparison of implant versus tooth-supported zirconia-based single crowns in a split-mouth design: a 4-year clinical follow-up study.

OBJECTIVES: This study aims to evaluate the 4-year clinical performance of tooth versus implant-supported single-unit zirconia crowns (LAVA™) placed on posterior region. MATERIALS AND METHODS: Twenty-four patients (10 men and 14 women) who had received 48 single crowns (24 implant-supported and 24 tooth-supported) from January 2007 to December 2009, were included. California Dental Association (CDA) quality assessment system, plaque and gingival index scores were used to evaluate the performance of the crowns at baseline and at all follow-up examinations. RESULTS: During the follow-up period, no fracture of zirconia coping has occurred. Major complication was chipping in three patients that required a new crown fabrication. Except for the failure ones, all crowns in both groups were rated as satisfactory at the follow-up examinations based on the CDA quality assessment criteria. There were no statistically significant differences between tooth and implant-supported crowns in terms of periodontal parameters. CONCLUSIONS: The present 4-year follow-up clinical study demonstrates that single-unit tooth- and implant-supported zirconia crowns have similar prosthetic and periodontal outcomes. CLINICAL RELEVANCE: Single-unit implant or tooth-supported zirconia crowns may be considered acceptable treatment modalities for restoration of either missing or compromised posterior teeth.

Forced eruption and implant site development in the aesthetic zone: A case report.

A multidisciplinary approach to develop the future implant site in the aesthetic zone was illustrated. A patient with perio-endo combined lesion at her upper central incisors was treated. Before extraction, forced eruption was performed and 12 months later, satisfactory amount of bone apposition was detected. At 2 weeks after atraumatic extraction, implants were placed and loaded with implant-supported restorations following osseous healing. Variables related to crown dimensions, periodontal/peri-implanter soft-tissue health and patient's aesthetic satisfaction were recorded at baseline, before extraction and after prosthetic treatment. At 12-month control, crown dimensions in the implant site were identical to the baseline and in addition to the healthy peri-implant tissues, successful aesthetics were obtained. Forced eruption is a successful non-invasive method to develop the aesthetics of the peri-implant tissues and implant-supported restorations.