Marginal fit of 3-unit CAD-CAM zirconia frameworks fabricated using cone beam computed tomography scans: an experimental study.

Whether cone beam computed tomography (CBCT) scans can be used for the fabrication of computer-aided design and computer-aided manufacturing (CAD-CAM) fixed dental prostheses (FDPs) is not known. The purpose of the present study was to compare the marginal fit of 3-unit zirconia FDPs fabricated by using CBCT or 3-dimensional (3D) laboratory scanning. Extracted second premolar and molar teeth in a maxillary typodont model were prepared. The first molar was removed and the typodont model was scanned with a laboratory or a CBCT scanner to generate two virtual 3D cast groups (3DL and CBCT). Forty four 3-unit zirconia FDPs were designed on virtual casts and milled. The vertical marginal discrepancy (VMD) was measured by ×100-magnification microscopy at seven locations on each abutment. A total of 616 measurements were made at 14 fixed locations in two groups of 22 specimens. The VMD data for 3DL and CBCT groups were statistically analyzed using the Mann-Whitney U test (α = 0.05). The mean VMDs on premolar ranged between 44 and 55 µm (median: 43-55 µm) in 3DL, and 74 and 100 µm (median: 72-93 µm) in CBCT; and on the molar, between 47 and 114 µm (median: 46-114 µm) in 3DL, and 91 and 162 µm (median: 93-156 µm) in CBCT. There was a significant difference between the gaps in 3DL and CBCT groups (p < 0.001). FDPs fabricated using 3D laboratory scanner had significantly smaller VMDs. Nevertheless, the 3-unit zirconia FDPs fabricated using CBCT scans presented promising marginal integrity.

Marginal fit of CAD-CAM monolithic zirconia crowns fabricated by using cone beam computed tomography scans.

STATEMENT OF PROBLEM: Information regarding the precision of monolithic zirconia crowns fabricated by using a standard computer-aided design and computer-aided manufacturing (CAD-CAM) workflow is available. However, information on the effect of a modified workflow using 3D laboratory scanning and/or cone beam computed tomography (CBCT) for monolithic zirconia crown fabrication is lacking. PURPOSE: The purpose of this in vitro study was to evaluate the effect of different scans on the marginal fit of CAD-CAM monolithic zirconia crowns fabricated by 3D laboratory scanning and CBCT. MATERIAL AND METHODS: An extracted maxillary left first molar was prepared and digitized by using a 3D laboratory scanner (D900; 3Shape A/S) (control group). The tooth was also scanned by CBCT (i-CAT; Imaging Sciences) to generate a second virtual 3D model (CBCTscan group). A tooth cast out of polyurethane (PU) (Zenotec Model; Wieland) was reproduced from the CBCT data by using a CAD software program (Dental System 2.6; 3Shape A/S) and milling machine (CORiTEC 550i; imes-icore) and further scanned by using the 3D laboratory scanner to generate a third virtual 3D model to represent a clinical scenario where a patient's cast is needed (PU3DLab group). A monolithic zirconia crown design (cement space: margin 40 µm, 1 mm above 70 µm) was used on the virtual models, and crowns were fabricated out of presintered zirconia blocks (ZenostarT4; Wieland) by using a 5-axis milling machine (CORiTEC 550i; imes-icore). The crowns were sintered (Sinterofen HT-S Speed; Mihm-Vogt), and the vertical marginal discrepancy (VMD) was measured by ×100-magnification microscopy. Measurements were made at 384 points in 3 groups of 16 specimens. The measurements for each specimen were averaged, and VMD mean values were calculated. The Kruskal-Wallis test was used for the statistical analysis (α=.05). The Mann-Whitney U test and Bonferroni adjustment were further used to compare the pairs (α=.017). RESULTS: The mean VMD value was 41 µm (median: 38 µm) for the control group, 44 µm (median: 42 µm) for the CBCTscan, and 60 µm (median: 58 µm) for the PU3DLab. No significant difference was found between control and CBCTscan groups (P=.274). However, there was a significant difference between control and PU3DLab and CBCTscan and PU3DLab groups (P<.001). CONCLUSIONS: Marginal fit of the crowns fabricated by using the 3D laboratory scanner and through the direct use of CBCT was better than that of the crowns fabricated by using the workflow that combined the use of CBCT, PU cast, and 3D laboratory scanner. All tested protocols enabled the fabrication of monolithic zirconia crowns with a marginal discrepancy smaller than 120 µm.

Marginal discrepancy of CAD-CAM complete-arch fixed implant-supported frameworks.

STATEMENT OF PROBLEM: Computer-aided design and computer-aided manufacturing (CAD-CAM) high-density polymers (HDPs) have recently been marketed for the fabrication of long-term interim implant-supported fixed prostheses. However, information regarding the precision of fit of CAD-CAM HDP implant-supported complete-arch screw-retained prostheses is scarce. PURPOSE: The purpose of this in vitro study was to evaluate the marginal discrepancy of CAD-CAM HDP complete-arch implant-supported screw-retained fixed prosthesis frameworks and compare them with conventional titanium (Ti) and zirconia (Zir) frameworks. MATERIAL AND METHODS: A screw-retained complete-arch acrylic resin prototype with multiunit abutments was fabricated on a typodont model with 2 straight implants in the anterior region and 2 implants with a 30-degree distal tilt in the posterior region. A 3-dimensional (3D) laboratory laser scanner was used to digitize the typodont model with scan bodies and the resin prototype to generate a virtual 3D CAD framework. A CAM milling unit was used to fabricate 5 frameworks from HDP, Ti, and Zir blocks. The 1-screw test was performed by tightening the prosthetic screw in the maxillary left first molar abutment (terminal location) when the frameworks were on the typodont model, and the marginal discrepancy of frameworks was evaluated using an industrial computed tomographic scanner and a 3D volumetric software. The 3D marginal discrepancy at the abutment-framework interface of the maxillary left canine (L1), right canine (L2), and right first molar (L3) sites was measured. The mean values for 3D marginal discrepancy were calculated for each location in a group with 95% confidence limits. The results were analyzed by repeated-measures 2-way ANOVA using the restricted maximum likelihood estimation and the Satterthwaite degrees of freedom methods, which do not require normality and homoscedasticity in the data. The between-subjects factor was material, the within-subjects factor was location, and the interaction was included in the model. Tukey tests were applied to resolve any statistically significant source of variation (overall α=.05). RESULTS: The 3D marginal discrepancy measurement was possible only for L2 and L3 because the L1 values were too small to detect. The mean discrepancy values at L2 were 60 µm for HDP, 74 µm for Ti, and 84 µm for Zir. At the L3 location, the mean discrepancy values were 55 µm for HDP, 102 µm for Ti, and 94 µm for Zir. The ANOVA did not find a statistically significant overall effect for implant location (P=.072) or a statistically significant interaction of location and material (P=.078), but it did find a statistically significant overall effect of material (P=.019). Statistical differences were found overall between HDP and the other 2 materials (P≤.037). CONCLUSIONS: When the tested materials were used with the CAD-CAM system, the 3D marginal discrepancy of CAD-CAM HDP frameworks was smaller than that of titanium or zirconia frameworks.

Effect of feldspathic porcelain layering on the marginal fit of zirconia and titanium complete-arch fixed implant-supported frameworks.

STATEMENT OF PROBLEM: Veneering with porcelain may adversely affect the marginal fit of long-span computer-aided design and computer-aided manufacturing (CAD-CAM) implant-supported fixed prostheses. Moreover, data regarding the precision of fit of CAD-CAM-fabricated implant-supported complete zirconia fixed dental prostheses (FDPs) before and after porcelain layering are limited. PURPOSE: The purpose of this in vitro study was to evaluate the effect of porcelain layering on the marginal fit of CAD-CAM-fabricated complete-arch implant-supported, screw-retained FDPs with presintered zirconia frameworks compared with titanium. MATERIAL AND METHODS: An autopolymerizing acrylic resin-fixed complete denture framework prototype was fabricated on an edentulous typodont master model (all-on-4 concept; Nobel Biocare) with 2 straight in the anterior and 2 distally tilted internal-hexagon dental implants in the posterior with multiunit abutments bilaterally in canine and first molar locations. A 3-dimensional (3D) laser scanner (S600 ARTI; Zirkonzahn) was used to digitize the prototype and the master model by using scan bodies to generate a virtual 3D CAD framework. Five presintered zirconia (ICE Zirkon Translucent - 95H16; Zirkonzahn) and 5 titanium (Titan 5 - 95H14; Zirkonzahn) frameworks were fabricated using the CAM milling unit (M1 Wet Heavy Metal Milling Unit; Zirkonzahn).The 1-screw test was applied by fixing the frameworks at the location of the maxillary left first molar abutment, and an industrial computed tomography (CT) scanner (XT H 225 - Basic Configuration; Nikon) was used to scan the framework-model complex to evaluate the passive fit of the frameworks on the master model. The scanned data were transported in standard tessellation language (STL) from Volume Graphics analysis software to PolyWorks analysis software by using the maximum-fit algorithm to fit scanned planes in order to mimic the mating surfaces in the best way. 3D virtual assessment of the marginal fit was performed at the abutment-framework interface at the maxillary right canine (gap 3) and right first molar (gap 4) abutments without prosthetic screws. The facial or buccal aspects of the teeth on frameworks were layered with corresponding porcelain (Initial Dental Ceramic System; GC) and CT-scanned again using the same protocol. Marginal fit measurements were made for 4 groups: titanium (Ti) (control), porcelain-layered titanium (Ti-P) (control), zirconia (Zir), and porcelain-layered zirconia (Zir-P). 3D discrepancy mean values were computed and calculated, and the results were analyzed with a repeated measures 3-way ANOVA using the maximum likelihood estimation method and Bonferroni adjustments for selected pairwise comparison t-tests (α=.05). RESULTS: The 3D fit was measured at gap 3 and gap 4. Statistically significant differences in mean 3D discrepancies were observed between Zir-P (175 µm) and Zir (89 µm) and between Zir-P and Ti-P (71 µm) (P<.001). CONCLUSIONS: Porcelain layering had a significant effect on the marginal fit of CAD-CAM-fabricated complete-arch implant-supported, screw-retained FDPs with partially sintered zirconia frameworks. 3D marginal discrepancy mean values for all groups were within clinically acceptable limits (<120 µm), except for the layered zirconia framework.

Effect of fabrication stages and cementation on the marginal fit of CAD-CAM monolithic zirconia crowns.

STATEMENT OF PROBLEM: Monolithic zirconia crowns fabricated using computer-aided design and computer-aided manufacturing (CAD-CAM) technology have recently become an alternative dental prosthetic treatment. The marginal fit of monolithic zirconia crown may be affected by different stages of the fabrication procedures in the laboratory and cementation. Information regarding the accuracy of fit of monolithic zirconia crowns at different stages of fabrication and cementation is limited. PURPOSE: The purpose of this in vitro study was to evaluate the effect of different stages of fabrication and cementation on the vertical marginal discrepancy (VMD) of CAD-CAM fabricated monolithic zirconia crowns. MATERIAL AND METHODS: Six ivorine right maxillary first molar typodont teeth with standardized anatomic preparations for complete coverage ceramic crowns were scanned with a 3-dimensional laboratory scanner. Crowns were designed using CAD software and milled from presintered monolithic zirconia blocks in a 5-axis dental milling machine. A cement space of 25 µm for the margins and a 50-µm space starting 1 mm above the finish lines of the teeth were virtually set in the CAD software. A total of 144 measurements were performed on 6 specimens with 8 measurement locations in 3 different stages using stereoscopic zoom microscopy; after initial production of the crowns (post-sintering group), after glazing (post-glazing group), and after cementation (post-cementation group). The VMD values were statistically analyzed with 1-way repeated measures ANOVA and the Holm-Sidak method (α=.05). RESULTS: Different stages of fabrication and cementation significantly affected the VMD of tested crowns (P=.003). The mean VMD was 38 µm for post-sintering group, 38 µm for post-glazing group, and 60 µm for post-cementation group, with statistical differences between the post-sintering group, the post-cementation group (P<.002), and the post-glazing group and post-cementation group (P<.003); there were no statistical differences between the post-sintering group and the post-glazing group (P=.966). CONCLUSIONS: Within the limitations of this in vitro study, glazing did not significantly change the VMD of CAD-CAM monolithic zirconia crowns. Cementation significantly increased the VMD values.

Effect of cement space on the marginal fit of CAD-CAM-fabricated monolithic zirconia crowns.

STATEMENT OF PROBLEM: Monolithic zirconia crowns fabricated with computer-aided design and computer-aided manufacturing (CAD-CAM) have recently become a common practice for the restoration of posterior teeth. The marginal fit of monolithic zirconia crowns may be affected by different cement space parameters set in the CAD software. Information is scarce regarding the effect of cement space on the marginal fit of monolithic zirconia crowns fabricated with CAD-CAM technology. PURPOSE: The purpose of this in vitro study was to evaluate the effect of cement space on the marginal fit of CAD-CAM-fabricated monolithic zirconia crowns before cementation. MATERIAL AND METHODS: Fifteen right maxillary first molar typodont teeth with standardized anatomic preparations for complete-coverage ceramic crowns were scanned with a 3-dimensional laboratory scanner. Crowns were designed 3-dimensionally using software and then milled from presintered monolithic zirconia blocks in a computer numerical control dental milling machine. The cement space was set at 25 µm around the margins for all groups, and additional cement space starting 1 mm above the finish lines of the teeth was set at 30 µm for group 25-30, 40 µm for group 25-40, and 50 µm for group 25-50 in the CAD software. A total of 120 images (3 groups, 5 crowns per group, 8 sites per crown) were measured for vertical marginal discrepancy under a stereoscopic zoom microscope and the data were statistically analyzed with 1-way analysis of variance, followed by the Tukey honestly significant difference test (α=.05). RESULTS: The results showed that different cement space values had statistically significant effect on the mean vertical marginal discrepancy value of tested crowns (P<.001). The mean marginal discrepancy was 85 µm for group 25-30, 68 µm for group 25-40, and 53 µm for group 25-50. CONCLUSIONS: Within the limitations of this in vitro study, it was concluded that the cement space had a significant effect on the marginal fit of CAD-CAM-fabricated monolithic zirconia crowns. The marginal fit improved as the cement space decreased.

Retrospective study on the 7.5-year survival of resin-bonded dental prostheses in single missing second premolar cases.

PURPOSE: The purpose of this study is to report retrospectively the clinical results of cast metal slot-retained resin-bonded fixed dental prostheses (RBFDPs) used in the restoration of single missing second premolar teeth, as this kind of prostheses provides acceptable clinical outcomes in a minimally invasive and esthetic treatment for the average patient requiring cheaper and faster treatment alternative for a single missing posterior tooth. However, the data present in the literature are scarce. MATERIALS AND METHODS: Clinical follow-up was reported up to 7.5 years in nine different cast metal slot-retained RBFDPs patients of both genders between 21 and 49 years of age. Routine clinical controls were performed 6 and 12 months after treatment, followed by regular intervals every year afterward. The Kaplan-Meier survival estimation method was used to determine the overall and functional survival rates and times of the RBFDPs at the end of the observation period. RESULTS: At the end of the follow-up, all of the RBFDPs were still functional with a mean follow-up of 6.7 years. The Kaplan-Meier estimation for the overall survival was calculated as 89% for up to 7.5 years with one failure due to debonding. The functional survival rate was 100% with the lowest and highest observation periods being 5.8 and 7.5 years, respectively. CONCLUSIONS: Within the limitations of this retrospective clinical study, it seems that the design and cementation regimen used for the RBFDPs presented can guarantee clinical success in the restoration of single missing second premolar teeth.

Amelogenesis Imperfecta: Rehabilitation and Brainstorming on the Treatment Outcome after the First Year.

Amelogenesis imperfecta (AI) affects enamel on primary and permanent dentition. This hereditary disorder is characterized by loss of enamel, poor esthetics, and hypersensitivity. Functional and cosmetic rehabilitation is challenging with variety of treatment options. This report presents the treatment of an AI patient using conventional fixed dentures and discusses issues related to posttreatment complications and prosthetic treatment outcome after 1 year of follow-up. A 19-year-old male AI patient with impaired self-esteem presented with hypersensitive, discolored, and mutilated teeth. Clinical examination revealed compromised occlusion and anterior open-bite. After hygiene maintenance full-coverage porcelain-fused-to-metal fixed restorations were indicated and applied. At the end of the treatment acceptable functional and esthetic results could be achieved. However, nearly a year after treatment a gingival inflammation in the esthetic zone complicated the outcome. Insufficient oral hygiene was to be blamed. Tooth sensitivity present from early childhood in these patients may prevent oral hygiene from becoming a habit. The relaxation due to relieve of hypersensitivity after treatment makes oral hygiene learning difficult. Continuous oral hygiene maintenance motivation may be crucial for the success of the treatment of AI patients. Treatment of AI patients should be carefully planned and an acceptable risk-benefit balance should be established.

A prospective cohort study on cast-metal slot-retained resin-bonded fixed dental prostheses in single missing first molar cases: results after up to 7.5 years.

PURPOSE: To evaluate under controlled clinical conditions the outcomes of cast-metal slot-retained resin-bonded fixed dental prostheses (RBFDPs) in which resin composite interlocked the restoration retainers in place after cementation in cases with single missing first molars, and to collect survival data on this esthetic RBFDP design combined with an economical metal fit-surface treatment method and resin luting system. MATERIALS AND METHODS: Forty-one tub-shaped inlay-retained RBFDPs were clinically observed for up to 7.7 years in 35 recipients of both genders between 18 and 52 years of age. Clinical examinations were performed at baseline and 6 and 12 months after restoration placement, and thereafter at regular 1-year intervals. Modified US Public Health Service (USPHS) parameters, sulcus bleeding index, Silness-Löe plaque index, pocket depths, tooth mobility, pulp vitality, and periapical radiographs regarding the abutment teeth were assessed at these follow-up appointments. The Kaplan-Meier survival estimation method was performed to detect the overall and functional survival rates and mean survival times of the RBFDPs at the end of the study. The Breslow (Generalized Wilcoxon) test was used to evaluate the influence of restoration location and age and gender of the patient regarding the overall survival probability at the end of the follow-up (α = 0.05). RESULTS: At the end of the study, 34 RBFDPs (83%) were still functioning with a mean follow-up of 6.3 years. According to the Kaplan-Meier survival curve, the overall and functional survival probabilities were calculated as 76% and 83%, with mean survival times of 6.8 years and 7.2 years, respectively. All clinical parameters monitored throughout the follow-up period predominantly revealed clinically acceptable results. Breslow test statistics presented nonsignificant differences with better results for the RBFDPs placed in the mandible of female recipients younger than 30 years of age. The most common failure noted with the RBFDPs was fracture of the occlusal veneering composite restoration over the retainer of a single abutment, leading to a predisposition of the restoration to partial debonding. CONCLUSION: Within the limitations of this prospective cohort study, it can be concluded that cast-metal slot-retained RBFDPs utilizing the interlocking mechanism of a resin composite to obtain additional retention from the abutment cavities show acceptable clinical success rates, and can be considered a minimally invasive, economical, and time-saving treatment alternative for the prosthetic rehabilitation of single missing first molars.

Directly fabricated inlay-retained glass- and polyethylene fiber-reinforced composite fixed dental prostheses in posterior single missing teeth: a short-term clinical observation.

PURPOSE: To evaluate the clinical usefulness of directly fabricated glass and polyethylene resin-bonded fiberreinforced composite (FRC) inlay-retained fixed dental prostheses (FDPs) in posterior single missing teeth over a short period of time. MATERIALS AND METHODS: Fourteen inlay-retained FRC FDPs with tub-shaped or box-shaped retainers were directly constructed in patients of both genders. A baseline examination was performed and the patients were examined regularly at 6-month intervals. The sulcus bleeding index, Silness-Löe plaque index, and probing depths of the abutments were checked regularly. Modified US Public Health Service (USPHS) parameters were used to compare the restorations at baseline and final examination. The Kaplan-Meier survival estimation method was performed to detect the overall survival rates and mean survival times of the restorations at the end of the follow-up. RESULTS: The length of the clinical observation was between 16 and 40 months for the FDPs still functioning after the end of the follow-up. No partial or total debonding of the prostheses or fracture of the frameworks was detected. Four veneering composite fractures at the veneer layer/fiber framework interface occurred in the pontic elements of 2 glass FRC FDPs and 2 polyethylene FRC FDPs after 6 and 10 months, and 20 and 22 months, respectively. Periodontal evaluation revealed clinically acceptable results, as did the USPHS evaluation. The overall survival curves of Kaplan-Meier at the end of the follow-up illustrated a 71% survival rate for the both glass and polyethylene FRC FDPs with mean survival times of 27 and 35 months, respectively. CONCLUSION: This study reported a mean period of service of 19 and 31 months for directly fabricated inlayretained glass and polyethylene FRC FDPs, respectively, with a 71% survival rate for the two framework constructions. Within the limitations of the study, these results can only be considered as preliminary. However, because of the lack of clinical data available for directly fabricated inlay-retained FRC FDPs, the results of this clinical observation may contribute to the still-evolving clinical knowledge of the FRC restorations.

A technique for fabrication of an interim ocular prosthesis.

Several ocular and orbital disorders require surgical intervention that may result in ocular defects. Immediate intervention is required to preserve the anophthalmic socket size and prevent scar tissue contractures that may follow surgery. Unfortunately, immediate fitting of an anophthalmic socket with an artificial eye may not always be possible, and a delayed prosthesis delivery may result in settling and sinking of the prosthesis into the socket, therefore requiring orbital cavity conformation. This article presents a short review of the most commonly used techniques for processing an ocular prosthesis, while suggesting a practical transition to the application of some of them. A technique for fabricating a custom-made provisional ocular prosthesis using digital imaging technology is described. This technique may be considered in order to avoid costly procedures that might be required as a result of delayed artificial eye insertion. The technique described in this article provides a cost-effective choice for optimal orbital cavity conformation and serves as a diagnostic aid for predicting the patient's compliance to ocular prosthetic treatment. The esthetic advantages and the relative ease of fabrication of this interim prosthesis allow it to be considered a first step in the management of untreated anophthalmic sockets.