Marginal adaptation of CAD-CAM onlays: Influence of preparation design and impression technique

Fracture Resistance of Direct versus Indirect Restorations on Posterior Teeth: A Systematic Review and Meta-Analysis

The aim of this systematic review and meta-analysis was to compare static compression forces between direct composite resin restorations and indirect restorations for posterior teeth. All studies comparing mechanical properties of direct versus indirect restorations of posterior teeth were included from 2007 up to February 2024. A meta-analysis was conducted for static compression fracture resistance. Medline, Central, and Embase databases were screened. Twenty-four articles were included in the qualitative synthesis, and sixteen studies were finally included in the quantitative synthesis. There was no difference in terms of fracture resistance between direct and indirect restorations for posterior teeth (p = 0.16 for direct and indirect composite resin restorations and p = 0.87 for direct composite resin restorations and indirect ceramic restorations). Also, sub-group analysis with or without cusp coverage in each group revealed no discernable difference. Based on this study, it can be concluded that the choice between direct and indirect restoration approaches may not significantly impact fracture resistance outcomes. There was no statically significant difference between direct and indirect restorations for posterior teeth in all cases of restorations with or without cusp coverage and no matter the used materials. However, to better evaluate these materials, further studies are warranted.

Evaluation of the accuracy of direct intraoral scanner impressions for digital post and core in various post lengths: An in-vitro study

STATEMENT OF PROBLEM

Despite the growing utilization of direct intraoral scanners (IOSs) in dentistry, there is a scarcity of research investigating their accuracy, specifically in post and core. Few studies have conducted comprehensive three-dimensional assessments and comparisons of IOSs with the conventional impression technique, particularly in different post space lengths.

PURPOSE

The purpose of this in vitro study was to digitally assess the accuracy of direct intraoral scanner (IOS) impressions for different post space lengths, specifically 6, 8, and 10 mm.

MATERIALS AND METHODS

A total of 45 typodont teeth (maxillary central incisors) were selected for this study. The teeth underwent endodontic treatment and were divided into three subgroups, each with 15 teeth, based on the desired post space lengths: 6, 8, and 10 mm. Intraoral scans of all specimens were acquired directly using the CEREC Primescan intraoral scanners by two trained examiners. The obtained scan data were compared with conventional impressions obtained using light and heavy bodies of polyvinyl siloxane (PVS). As a control, the conventional impressions were subsequently scanned using an inEos X5a lab scanner. The accuracy of the digital scans was evaluated in the coronal, middle, and apical thirds using the Geomagic Control X software. Statistical analysis was performed using Bonferroni Post-hoc and One-way ANOVA tests to analyze the data.

RESULTS

The overall mean root mean square (RMS) deviations for the different post lengths across the three thirds groups were 58, 81, and 101 μm for the 6, 8, and 10 mm subgroups, respectively. There were no statistically significant differences in the accuracy of the coronal and middle thirds among all subgroups (p > 0.5). However, in the apical third, the 10 mm subgroup exhibited a significantly lower accuracy (163 μm) compared to the 6 mm (96 μm) and 8 mm (131 μm) subgroups (p < 0.05). These results suggest that while the accuracy of intraoral scans using direct IOS impressions was consistent in the coronal and middle thirds regardless of the post length, there was a noticeable decrease in accuracy in the apical third, particularly with longer post lengths.

CONCLUSION

Considering the limitations of this in vitro study, chairside direct IOS impressions offer a viable and clinically acceptable alternative to the conventional impression technique for post space lengths of 6 and 8 mm. However, as the post space length preparation increases, the accuracy of IOS decreases.

CLINICAL SIGNIFICANCE

The Chairside direct IOS enables expedited and efficient digital impression capture within the root canal, ensuring acceptable accuracy for intracanal post length preparation of up to 8 mm.

Is the digital workflow more efficient for manufacturing partial-coverage restorations? A systematic review

STATEMENT OF PROBLEM

A consensus on whether a fully digital workflow can replace conventional methods of manufacturing partial-coverage restorations is lacking.

PURPOSE

The purpose of this systematic review was to evaluate the accuracy, fit, and clinical outcomes of inlay, onlay, overlay, and endocrown restorations obtained with both digital and conventional workflows.

MATERIAL AND METHODS

This study complied with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and was registered in the International Prospective Register of Systematic Reviews database (CRD42021258696). Studies evaluating the accuracy, fit, and clinical outcomes of inlay, onlay, overlay, and endocrown restorations obtained with digital and conventional workflows were included from 5 databases searched in November 2022. The Checklist for Reporting Randomized Clinical Studies (ROB 2) and the Checklist for Reporting In vitro Studies (CRIS guidelines) were used to assess the risk of bias.

RESULTS

Twenty-three studies were included in this review. Sixteen studies evaluated marginal and internal fit, 5 evaluated accuracy, 3 evaluated fracture resistance, and 1 evaluated long-term clinical performance. Although most studies reported acceptable clinical outcomes for both workflows, 11 studies showed better results with the conventional workflow, 10 with the digital workflow, and 2 reported that the outcomes of the workflows were similar.

CONCLUSIONS

Clinically acceptable values have been reported for the parameters evaluated in both digital and conventional workflows, and no consensus has been reached regarding the more efficient method.

Assessment Methods for Marginal and Internal Fit of Partial Crown Restorations: A Systematic Review

BACKGROUND

Different methods are used for the analysis of marginal and internal fit of partial crowns, but not all of them are applicable for in vivo studies. The aim of this review is to search the available methods, described in the current literature, to assess marginal and internal fit in partial crowns.

METHODS

an electronic search was performed on Pubmed and Web of Science databases to find studies published from 1 January 2017 up to 2 March 2023, following PRISMA guidelines and Cochrane handbook for systematic reviews. The search strategy applied was: "(marginal) AND (fit OR gap OR adaptation OR discrepancy) AND (inlay OR onlay OR partial crown)". In vitro studies which evaluated marginal and internal fit on CAD CAM or 3D printed partial crowns were included in this review. Quality of the studies was assessed by using Quality Assessment Tool For In Vitro Studies (QUIN tool).

RESULTS

22 studies were included. Among conventional methods, direct view with microscope, indirect view on resin replicas, and silicone replica technique (SRT) were used. Considering new digital methods, micro-CT, SRT 3D and triple scan technique (TST) were applied.

CONCLUSIONS

Among 2D methods, direct view technique is the most used marginal fit analysis. For a more comprehensive evaluation, a 3D digital analysis is suggested. SRT and indirect view are the only 2D methods available for in vivo analysis. A protocol for the application of TST for assessment in vivo is now available, but no studies are reported in literature yet.

Effect of three different preparation designs on the marginal adaptation of indirect overlay restoration fabricated from lithium disilicate ceramic material: An in-vitro comparative study

Objectives

Marginal adaptation is considered one of the key factors influencing the success of indirect restorations. This study aimed to estimate the marginal fit of lithium disilicate overlays with three distinct preparation designs before and after cementation.

Methods

Thirty maxillary first premolars were divided into the hollow chamfer design (HCD) group, butt-joint design (BJD) group, and conventional occlusal box design (COD) group (n = 10 each). The samples were scanned using an intra-oral scanner, and overlays were fabricated using computer-assisted design and milled on a computer-assisted machine. The finished restorations were luted using a self-adhesive resin RelyX Ultimate. The marginal gap was assessed using a digital microscope with 230X magnification power. Statistical analysis was conducted using analysis of variance and post hoc (Bonferroni correction) tests, assuming a significance level of 5%.

Results

The HCD and BJD groups recorded significantly lower marginal gap, (11.39 ± 0.72, 16.29 ± 0.75) and (11.59 ± 0.75, 16.93 ± 0.65) respectively, than the COD group (24.57 ± 1.18, 34.45 ± 1.09) both pre- and post-cementation.

Conclusion

This study demonstrated that modification of tooth preparation plays a significant role in the marginal adaptation of the lithium disilicate overlays. The gap was smaller with the HCD and BJD than with the COD, with a statistically significant difference.

Effect of preparation type on the accuracy of different intraoral scanners: An in vitro study at different levels of accuracy evaluation

OBJECTIVE

Evaluation of the effect of preparation type (inlay, onlay, and crown) on the accuracy of different intraoral scanning (IOS) systems at the preparation and arch segment levels.

MATERIALS AND METHODS

Three molars were prepared for inlay, onlay, and crown. Each preparation was scanned 10 times by CEREC Omnicam, Trios 3 (TS), and Medit i500 scanners. Each image was trimmed twice. The first trimming produced a preparation image (PI), and the second trimming extracted a segment image (SI) that involved the preparation with the adjacent teeth. Trueness and precision were calculated at the PI and SI levels.

RESULTS

At the PI level, all IOS systems had similar trueness pattern for all preparations, where the inlay had the best trueness followed by the crown and onlay. At the SI level, the different preparations showed similar trueness. The precision did not show a clear pattern of superiority for any preparation. The TS was significantly more precise than other IOS systems at the PI and SI levels, for every preparation. The proximal areas suffered from the greatest errors, regardless of preparation type.

CONCLUSIONS

The preparation type influenced PI trueness, and the IOS system affected PI and SI precisions.

CLINICAL SIGNIFICANCE

The smaller and less complex preparations have greater IOS accuracy than larger and more complex preparations. As the proximal areas are more affected regardless of the preparation, a more accessible proximal area for scanning is desirable.

Triple scan evaluation of internal and marginal adaptation of overlays using different restorative materials

OBJECTIVE

Problems in the confection of indirect restorations may increase the marginal and internal gap. This study aimed to quantify the marginal and the internal fit of overlays fabricated with three different materials.

MATERIALS AND METHODS

Standardized cavities were prepared on endodontically treated human third molars and digital impressions were done using an intraoral camera (Trios 3). Restorations were designed (n = 15) and fabricated with three materials: Hybrid ceramic (Cerasmart; GC Corp, EUROPE), high-strength lithium disilicate (GC Initial® LiSi Press; GC Corp, Tokyo, Japan), and zirconia reinforced Lithium Silicate Glass Ceramic (Vita Suprinity; Vita, Germany). Axial, marginal, pulpal, and gingival gaps were calculated by measuring the distance between the restoration and the tooth at several reference points. Two-Way analysis of variance was used for statistical analysis. The significance level was set at α = 0.05.

RESULTS

Mean gap was significantly influenced by the material (p < 0.001), gap localization (p < 0.001), and interaction between the factors (p = 0.002). For all materials, the highest gap was observed at gingival and pulpal surfaces (p ≤ 0.015). LiSi Press achieved the overall lowest values at axial values measurements (p ≤ 0.003).

CONCLUSIONS

The performance of a CAD/CAM system relative to marginal adaptation is influenced by the restorative material used. High-strength lithium disilicate seems to be showed the best marginal adaptation.

CLINICAL SIGNIFICANCE

Marginal and internal adaptation of CAD/CAM restorations could be influenced by the type of material chosen.

Fracture Resistance of Sintered Monolithic Zirconia Dioxide in Different Thermal Units

The purpose of this study was to compare the fracture strength of monolithic zirconium dioxide subjected to a sintering process in two different furnaces: InFire HTC Speed and CEREC SpeedFire. Methods: Forty restorations were designed and machined using a computer aided design / computer aidded machine (CAD/CAM) system. The restorations were randomly assigned to two groups of 20 samples each, Group 1 for the SpeedFire furnace (fast sintering) and Group 2 for the InFire furnace (slow sintering). Each of the crowns was subjected to a maximum compression load recorded in Newtons (N) and a displacement control with a speed of 1 mm/min. Results: Group 1 presented an average of 1222.8 N and a standard deviation of 136.91 N. Group 2 obtained a mean of 1068.5 N and a standard deviation of 316.39 N. Conclusions: There were no significant differences between the two groups, and the mechanical strength of the material was not affected, which would imply a saving of clinical and laboratory time when performing rapid sintering on monolithic translucent zirconium dioxide restorations. However, rapidly sintered restorations have limited reliability.

Effect of Die Materials on Marginal and Internal Adaptation of Zirconia Copings: An In Vitro Study

Aim:

Close adaptation of cemented CAD/CAM restorations to their abutments is highly dependent on precise impressions and accurate replicas of teeth and adjacent oral tissues. This in-vitro study compared the effect of two die materials, as physical replicas of prepared teeth, on internal and marginal adaptations of zirconia copings to their corresponding abutments.

Materials and Methods:

A virtual model simulating a prepared premolar was designed and used for the milling of thirty identical metal models. Impression was taken of all models by Polyvinyl siloxane material. Fifteen impressions were poured in with Type IV stone and the other fifteen with polyurethane resin to make dies. All dies were scanned, and for each of them, zirconia coping was designed and milled. The copings were cemented to their corresponding metal models. Marginal gap between each coping and its metal model was measured at 20 points with a stereomicroscope (×60). Then the specimens were sectioned into two halves, and the internal gap was measured at seven points, including right and left cervico-axial, mid-axial, occluso-axial, and mid-occlusal. The data were analyzed with an independent T-test and repeated measure ANOVA at a 95% confidence level (p<0.05).

Results:

Mean value of marginal gap for Type IV stone and Exakto-Form groups were 54.31 ± 4.11 μm and 56.25 ± 4.24 μm, respectively. Mean values of the internal gaps for both groups ranged from 48 μm to 120 μm.

Conclusion:

Based on the results of this study, an internal and marginal adaptation of zirconia copings designed on digitized polyurethane and Type IV stone dies are clinically acceptable.

Functional or Nonfunctional Cusps Preservation for Molars Restored with Indirect Composite or Glass-Ceramic Onlays: 3D FEA Study

Evidence regarding the effect of the onlay preparation design for different CAD/CAM restorative materials considering the preservation of cusps is lacking. Molars were 3D-modeled in four preparation designs for onlay restoration: traditional design with functional cusp coverage (TFC), non-retentive design with functional cusp coverage (NFC), traditional design with non-functional cusp coverage (TNFC) and non-retentive design with non-functional cusp coverage (NNFC). The restorations were simulated with two CAD/CAM restorative materials: LD—lithium disilicate (IPS e.max CAD) and RC—resin composite (GrandioBloc). A 100 N axial load was applied to the occlusal surface, simulating the centric contact point. Von Mises (VM) and maximum principal (Pmax) stress were evaluated for restorations, cement layer and dental substrate. The non-retentive preparation design reduced the stress concentration in the tooth structure in comparison to the conventional retentive design. For LD onlays, the stress distribution on the restoration intaglio surface showed that the preparation design, as well as the prepared cusp, influenced the stress magnitude. The non-retentive preparation design provided better load distribution in both restorative materials and more advantageous for molar structure. The resin composite restoration on thenon-functional cusp is recommended when the functional cusp is preserved in order to associate conservative dentistry and low-stress magnitude.

A comparison of the marginal adaptation of composite overlays fabricated with silicone and an intraoral scanner

Background

Intraoral scanners have been developing during last years. The aim of this study was to know if digital impressions achieve a marginal adaptation in overlays as well as conventional impressions with silicone.

Material and Methods

Sixty-two extracted molars were selected. The samples were prepared for MOD overlays. The teeth were divided into two groups (n=31). Group 1: impressions were made with silicone (Express™ Impression, 3M ESPE) and overlays were manufactured with Sinfony composite (3M ESPE) by the laboratory technician. Group 2: impressions were taken with the scanner True Definition (TD, 3M ESPE) and under Lava Ultimate CAD/CAM Restorative composite (3M ESPE) were produced the restorations. Under 32x magnification images of vestibular, lingual, mesial and distal were capture in all the samples. Then the fit of the restorations was evaluated before and after cementation. Data were analysed statistically applying ANOVA and Bonferroni test.

Results

The marginal gap was better in TD group before (169,76 ± 54,15 µm) and after (145,16 ± 57,89 µm) cementation than in the silicone group (190,89 ± 58,18 µm) (187,47 ± 81,29 µm). The lowest marginal gap was in oclusal surface and the higher value was in the proximal margin for all the groups.

Conclusions

Digital impressions regarding marginal adaptation achieve better results than conventional impressions.

Key words:Composite onlays, overlays, restorative, CAD/CAM, intraoral scanner, silicone impressions, marginal adaptation.

Step-by-Step Esthetic Rehabilitation with Chairside System

In modern dentistry, Computer-Aided Design and Manufacturing (CAD/CAM) is a promising technology that allows fabrication of prosthetic restorations through milling procedures. Over years, with the continuous improvement of technology, direct CAD/CAM or “chairside” technology is becoming a widespread approach which offers immediate rehabilitation with long-term rates reported by several studies compared to conventional techniques. All steps are generally carried out in the dental office during the same treatment session. The present paper is about a healthy female patient with a decayed 36 tooth which was restored by ceramic onlay using Planmeca's PlanCAD system. Through the present clinical case, a detailed protocol of chairside technology would be presented from the digital impression to the milling process. It would detail impression steps. It would also highlight especially the virtual design confection of prosthetic restoration using a biogeneric model included in the software. It also illustrated tools which could be used by the dentist to perform the design. Also, some useful tips would be presented in order to perform the confection. On this subject, various studies showed the viability of such technology. To summarize, referring to previous studies, this promising technology allows especially time-saving and patient's comfort compared to the indirect one.

Local accuracy of actual intraoral scanning systems for single-tooth preparations in vitro

BACKGROUND

The authors evaluated the local accuracy of intraoral scanning (IOS) systems for single-tooth preparation impressions with an in vitro setup.

METHODS

The authors digitized a mandibular complete-arch model with 2 full-contour crowns and 2 multisurface inlay preparations with a highly accurate reference scanner. Teeth were made from zirconia-reinforced glass ceramic material to simulate toothlike optical behavior. Impressions were obtained either conventionally (PRESIDENT, Coltène) or digitally using the IOS systems TRIOS 3 and TRIOS 3 using insane scan speed mode (3Shape), Medit i500, Version 1.2.1 (Medit), iTero Element 2, Version 1.7 (Align Technology), CS 3600, Version 3.1.0 (Carestream Dental), CEREC Omnicam, Version 4.6.1, CEREC Omnicam, Version 5.0.0, and Primescan (Dentsply Sirona). Impressions were repeated 10 times per test group. Conventional (CO) impressions were poured with type IV gypsum and digitized with a laboratory scanner. The authors evaluated trueness and precision for preparation margin (MA) and preparation surface (SU) using 3-dimensional superimposition and 3-dimensional difference analysis method using (95% - 5%) / 2 percentile values. Statistical analysis was performed using Kruskal-Wallis test. Results were presented as median (interquartile range) values in micrometers.

RESULTS

The authors found statistically significant differences for MA and SU among different test groups for both trueness and precision (P < .05). Median (interquartile range) trueness values ranged from 11.8 (2.0) μm (CO) up to 40.5 (10.9) μm (CEREC Omnicam, Version 5.0.0) for SU parameter and from 17.7 (2.6) μm (CO) up to 55.9 (15.5) μm (CEREC Omnicam, Version 5.0.0) for MA parameter.

CONCLUSIONS

IOS systems differ in terms of local accuracy. Preparation MA had higher deviations compared with preparation SU for all test groups.

PRACTICAL IMPLICATIONS

Trueness and precision values for both MA and SU of single-unit preparations are equal or close to CO impression for several IOS systems.

Effect of tooth preparation design on marginal adaptation of composite resin CAD-CAM onlays

STATEMENT OF PROBLEM

Although different preparation designs have been proposed for onlays fabricated by computer-aided design and computer-aided manufacturing (CAD-CAM), their effect on marginal adaptation is unclear.

PURPOSE

The purpose of this in vitro study was to investigate the effect of tooth preparation designs on the marginal and internal adaptation of ceramic-reinforced composite resin CAD-CAM onlays.

MATERIAL AND METHODS

A traditional preparation with a heavy chamfer on the functional cusp and a contrabevel on the nonfunctional cusp and a shoulder preparation with equal reduction on all cusps were used for mesial-occlusal-distal (MOD) onlay preparations. Ceramic-reinforced composite resin onlays were designed and milled based on the scanned prepared teeth. A digital silicone replica technique was used to determine marginal discrepancies between preparations and onlay restorations. A total of 100 numeric distances (representations of the fit in each region) were measured in 3 distinct regions: the buccal margin, lingual margin, and internal area. Independent Student t tests were used to determine significant differences (α=.05).

RESULTS

Traditional preparation designs resulted in significantly smaller overall discrepancies (50.9 ±0.5 μm and 139.1 ±5.4 μm, P<.001) and smaller marginal discrepancies in the buccal (49.7 ±1.4 μm and 135.8 ±2.2 μm, P<.001) and lingual areas (47.1 ±1.0 μm and 133.4 ±1.1 μm, P<.001).

CONCLUSIONS

The marginal adaptation of ceramic-reinforced composite resin CAD-CAM onlays was affected by the preparation design. The traditional preparation design offered better marginal adaptation; therefore, it is recommended in clinical practice.

The marginal discrepancy of lithium disilicate onlays: Computer-aided design versus press

Aim:

The aim of the study was to evaluate and compare the vertical marginal discrepancy of computer-aided design (CAD)/computer-aided manufacturing (CAM) and pressable lithium disilicate onlays.

Materials and Methods:

A maxillary first premolar typodont tooth was prepared to receive lithium disilicate onlay. Mesio-occluso-distal cavity was prepared with palatal cusp reduction and collar preparation. In the proximal box, gingival seat was placed 1 mm coronal to the cementoenamel junction and mesiodistal width of the seat was kept to 1 mm. Thirty stone models were prepared from thirty rubber base impressions and divided into two groups, based on the technique of fabrication of onlays: (1) Group CL (CAD/CAM lithium disilicate) and (2) Group PL (Pressable lithium disilicate). Fifteen onlays per each group were fabricated by following the manufacturer instructions. Marginal fit of all the samples were analyzed by using stereomicroscope with Image Analysis software. Statistical analysis was done by t-test.

Results:

Statistical significant difference was found between both the groups. The lowest marginal discrepancy (41.46 μm) was measured for Group CL (CAD/CAM lithium disilicate) specimens, and the highest (55.95 μm) discrepancy was observed on the Group PL (Pressable lithium disilicate) specimens.

Conclusion:

Although there was a statistically significant difference between the two groups, marginal gap of both the groups were in clinically acceptable levels.