Effect of ceramic materials and tooth preparation design on computer-aided design and computer-aided manufacturing endocrown adaptation and retentive strength: An in vitro study

OBJECTIVES

To evaluate how various tooth preparation designs impact the adaptation-both at the margins and internally-and the retentive strength of computer-aided design and computer-aided manufacturing (CAD/CAM) produced endocrowns.

MATERIALS AND METHODS

60 extracted human mandibular first molars were endodontically treated and assigned into three groups (n = 20) according to the tooth preparation design: Group N: butt joint design, Group F and F1 received 1- and 2-mm circumferential ferrule preparation, respectively. Endocrowns were milled using either lithium disilicate glass-ceramic (IPS emax ceramic) or monolithic zirconia. The internal and marginal adaptation of the endocrowns were evaluated using the replica technique. After cementation, the endocrowns of all test groups were dislodged axially at 0.5 mm/min using a universal testing machine. A 2-way ANOVA and the independent samples t-test (α = .05) were performed to statistically analyze the data.

RESULTS

The effect of changing the design of the tooth preparation (butt joint, ferrule) on the marginal and internal gap was shown to be statistically significant (p < .05); the lower gap values were recorded at the axial followed by cervical, marginal, and pulpal floor walls in both ceramic groups regardless of the teeth preparation design. The ANOVA test revealed similar average removal forces and stresses for the two types of tested ceramic materials.

CONCLUSION

IPS emax ceramic adapted better than monolithic zirconia ceramic, regardless of the preparation design. Ferrule preparation design is more retentive than butt joint preparation, regardless of the type of ceramic material used.

The effect of preparation design on fracture resistance of endodontically treated maxillary premolars restored with lithium disilicate computer-aided design/computer-aided manufacturing endocrowns: An in vitro study

Purpose

This study aimed to assess the effect of preparation design on fracture resistance (FR) of endodontically treated maxillary premolars restored with lithium disilicate (LDS) endocrowns fabricated by the computer-aided design/computer-aided manufacturing (CAD/CAM) technology.

Materials and Methods

In this in vitro, experimental study, 30 sound maxillary premolars were randomly assigned to three groups (n = 10) of control (no preparation), endocrown preparation with butt-joint design without ferrule, and endocrown preparation with ferrule (shoulder design with 1 mm height). After restoration fabrication and cementation, the teeth underwent thermocycling, were mounted with 45° angle, and subjected to compressive load in a universal testing machine to measure their FR. The mode of failure was also determined under a stereomicroscope. Data were analyzed using one-way ANOVA and Tukey's test (α =0.05).

Results

The shoulder group showed the highest FR (1768.98 ± 386.1 N). The difference in FR was statistically significant among the three groups (P < 0.05). Pairwise comparisons revealed that the shoulder group had significantly higher FR than the butt-joint (P = 0.001) and control (P = 0.009) groups. However, the difference in FR between the butt-joint and control groups was not significant (P = 0.75). The mode of failure was not significantly different among the three groups (P > 0.05).

Conclusions

Preparation design had a significant effect on FR of endodontically treated maxillary premolars restored with LDS CAD/CAM Endocrowns, such that addition of a short axial wall in shoulder group significantly increased the FR of endocrowns.

Clinical performance of two onlay designs for molars after root canal treatment

PURPOSE

To evaluate the clinical performance of two proposed onlay designs.

METHODS

Molars with occlusal and/or mesial/distal defects after root canal treatment were classified by design into three groups. Onlays without shoulders were the control group (Group C, n = 50). The designed onlays were Group O (n = 50) and the designed mesio-occlusal/disto-occlusal onlays were Group MO/DO (n = 80). All onlays had an occlusal thickness of approximately 1.5-2.0 mm, and the designed onlays had a shoulder depth and width of approximately 1 mm. In Groups C and O, the box-shaped retention was 1.5 mm in depth. The proximal box was connected with a dovetail retention in Group MO/DO. Patients were examined every 6 months and followed for 36 months. Restorations were evaluated by using the modified United States Public Health Service Criteria. Statistical analysis was performed by using Kaplan-Meier analysis, the chi-square test, and Fisher's exact test.

RESULTS

No tooth fracture, debonding, secondary caries, or gingivitis was observed in any group. Groups O and MO/DO had satisfactory survival and success rates, and there was no significant difference in performance characteristics among the three groups (P > 0.05).

CONCLUSION

The two proposed onlay designs were effective in protecting molars.

Post-Fatigue Fracture Resistance of Lithium Disilicate and Polymer-Infiltrated Ceramic Network Indirect Restorations over Endodontically-Treated Molars with Different Preparation Designs: An In-Vitro Study

The aim of the present study was to evaluate the fatigue to cyclic and static resistance of indirect restorations with different preparation designs made either of lithium disilicate (LS) or polymer-infiltrated ceramic network (PICN). Eighty-four (n = 84) molars were chosen, endodontically treated, and prepared with standardized MOD cavities. The molars were randomly divided into 6 study groups (n = 14) taking into account the "preparation design'' (occlusal veneer with 1.2 mm occlusal thickness; overlay with 1.6 mm occlusal thickness; adhesive crown with 2 mm occlusal thickness) and the "CAD/CAM material'' (E-max CAD, Ivoclar vivadent; Vita Enamic, Vita). A fatigue test was conducted with a chewing simulator set at 50 N for 1,500,000 cycles. Fracture resistance was assessed using a universal testing machine with a 6 mm diameter steel sphere applied to the specimens at a constant speed of 1 mm/min. A SEM analysis before the fracture test was performed to visually analyze the tooth-restoration margins. A statistical analysis was performed with a two-way ANOVA and a post-hoc pairwise comparison was performed using the Tukey test. The two-way ANOVA test showed that both the preparation design factor (p = 0.0429) and the CAD/CAM material factor (p = 0.0002) had a significant influence on the fracture resistance of the adhesive indirect restorations. The interaction between the two variables did not show any significance (p = 0.8218). The occlusal veneer had a lower fracture resistance than the adhesive crown (p = 0.042) but not lower than the overlay preparation (p = 0.095). LS was more resistant than PICN (p = 0.002). In conclusion, in the case of endodontically treated teeth, overlay preparation seems to be a valid alternative to the traditional full crown preparation, while occlusal veneers should be avoided in restoring non-vital molars with a high loss of residual tooth structure. LS material is more resistant compared to PICN.

Effect of preparation design on marginal adaptation and fracture strength of ceramic occlusal veneers: A systematic review

OBJECTIVES

This systematic review aims to investigate the effect of different preparation designs on the marginal fit and fracture strength of ceramic occlusal veneers.

MATERIALS AND METHODS

Based on the PICO question and the search terms, an electronic search was performed in Google Scholar, PubMed (MEDLINE), Scopus, Cochrane Library, Web of Science, Science Direct, Wiley, Ovid, and SAGE for articles published up to July 2022. After including English in vitro studies that evaluated posterior ceramic occlusal overlays at the posterior with ceramic restorations by following the PRISMA statement, the extracted data was tabulated. The methodological quality of the included studies was evaluated. Risk of bias assessment was done independently by two authors using the modified MINORS scale.

RESULTS

About 3138 search results were screened, of which 22 were selected due to their titles. Twenty-one full-text articles were assessed for eligibility. Seventeen in-vitro studies were finalized for the extraction of quantitative data. All 17 articles had a low risk of bias and were retained. The influencing items for evaluating the research were different in most studies; therefore, qualitative synthesis of the results was feasible. They generally included preparation design, material thickness, depth of preparation in the tooth, internal divergence angle, and finish line. Meta-analysis was not done due to heterogeneity of preparation types and evaluation methods. Results revealed that fracture resistance of occlusal veneers is higher than normal mastication force, and it is sufficient to prepare the occlusal surface, use a self-etching primer for bonding, and an acceptable minimum ceramic thickness. The marginal discrepancy of occlusal veneers is clinically acceptable. However, this systematic review faces some limitations due to the lack of in vivo studies, different preparation designs in included studies, different follow-ups, and lack of comprehensive explanations in articles.

CONCLUSIONS

The preparation design of occlusal veneers influences both marginal adaptation and fracture resistance. Various preparation designs are proven to have clinically acceptable fracture strength and marginal adaptation.

Impact of Ceramic Material and Preparation Design on Marginal Fit of Endocrown Restorations

Background: The aim of this study is to investigate the impact of ceramic material and preparation design on the marginal fit of endocrown restorations. Methods: Forty endocrown restorations were CAD/CAM-fabricated for forty extracted maxillary first premolar teeth. Samples were divided into two groups (n = 20) according to the ceramic materials used: Celtra Duo and Vita Enamic. Each group was divided into two subgroups (n = 10) according to the preparation design: with no intraradicular extension and with 3 mm intraradicular extension. The marginal gap was examined using a digital microscope. Results: Celtra Duo without intraradicular extension recorded the least mean marginal gap (7.74 ± 1.55 µm), while Group Celtra Duo with 3 mm intraradicular extension recorded the highest mean marginal gap (29.54 ± 6.32 µm). Group Vita Enamic recorded a lesser marginal gap (18.03 ± 12.11 µm) than group CD (Celtra Duo) (18.64 ± 12.05 µm). There is a statistically non-significant difference between the two groups of materials (p = 0.873). There is a statistically significant difference between the two tested preparation designs (p < 0.001). Conclusion: All groups recorded a marginal gap within clinically accepted values. Material selection may influence the fitting of restorations. Intraradicular extension for endocrown restorations adversely affects the marginal fit, however, the marginal gap is still within the clinically accepted range.

Effect of Luting Cement and Convergence Angle of the Preparation on the Internal Fit of Zirconia Restorations

The objective was to evaluate the effect of luting agents and the preparation design on the internal fit of zirconia restorations. Sixty dies were prepared and divided in occlusal convergence angle of 6° (OC6) and 12° (OC12). CAD/CAM zirconia copings were fabricated (Lava All-Ceramic System). A zinc phosphate cement (ZPC); a glass ionomer cement (GIC); and a resin cement (RC) were studied. Specimens were sectioned and coping/die discrepancies were evaluated through Stereoscopic Microscopy. A closer fit was observed in OC12 when compared to OC6 (p < 0.001). For OC6 no significant differences were observed in between ZPC, GIC, and RC (p > 0.05). For OC12, a significantly closer fit was recorded on the ZPC subgroup when compared to the GIC subgroup (p < 0.001). Preparations of 12 degrees demonstrated a closer internal fit when compared to 6 degrees. Preparations of 12 degrees achieved better internal fit values with ZPC (Fortex) followed by RC (RelyX Unicem), and GIC (Ketac Cem). No differences were found when comparing different luting agents over 6° degrees preparations.

Effect of incisal preparation design on load-to-failure of ceramic veneers

OBJECTIVE

This in vitro study aims to evaluate load-to-failure of ceramic veneers with butt joint (BJ) and feathered edge (FE) incisal preparation designs, and to correlate these results to the failure mode of the restorations.

MATERIALS AND METHODS

One hundred and forty-eight typodont teeth (customized Nissin A25A-UL19B) were divided into two different preparation configurations BJ and FE and two different loading angulations, 0° and 20°. Lithium disilicate ceramic veneers (IPS e.max CAD, Ivoclar Vivadent) were milled using computer-aided-design-and-computer-aided-manufacturing (CAD/CAM) techniques. Veneers were bonded to typodont teeth with resin cement (IPS Variolink Esthetic, Ivoclar Vivadent). Each group was loaded at the incisal edge using an Instron Universal Testing Machine at a crosshead speed of 0.01 mm/s till failure.

RESULTS

Pairwise comparison showed veneers from the BJ groups had a significantly higher load-to-failure value compared to the FE groups. Veneers with a FE preparation design loaded at 20° angulation had the lowest load-to-failure value.

CONCLUSIONS

Within the limitations of the present study, both incisal preparation designs and loading angulations have significant effects on the load-to-failure values of ceramic veneers. BJ group exhibits a significantly higher load-to-failure value compared to the FE group.

CLINICAL SIGNIFICANCE

BJ incisal preparation is preferred over FE preparation design.

Fracture Resistance of Various Thickness e.max CAD Lithium Disilicate Crowns Cemented on Different Supporting Substrates: An In Vitro Study

PURPOSE

To investigate the influence of abutment material properties on the fracture resistance and failure mode of lithium disilicate (IPS e.max) CAD/CAM (computer-aided design/manufacturing) crowns on traditionally and minimally prepared simulated tooth substrates.

MATERIALS AND METHODS

Thirty lithium disilicate (IPS e.max) CAD/CAM crowns were divided into three groups (n = 10): TD: traditional thickness crowns cemented on Paradigm MZ100 abutments; MD: minimal thickness crowns cemented on Paradigm MZ100 abutments; ME: minimal thickness crowns cemented on e.max abutments. The 3Shape system was used to scan, design and mill all abutments and crowns with a die space set to 40 µm. Traditional thickness crowns were designed based on manufacturer guidelines with 1.5 mm occlusal thickness and 1.0 mm margins. Minimal thickness crowns were designed with 0.7 mm occlusal thickness and 0.5 mm margins. MZ100 composite and e.max abutments were selected to simulate dentin and enamel substrates, respectively, based on their elastic-modulus. Variolink Esthetic was used to cement all samples following manufacturer's instructions. A universal testing machine was used to load all specimens to fracture with a 3 mm radius stainless steel hemispherical tip at a crosshead speed 0.5 mm/minute along the longitudinal axis of the abutment with a 1 mm thermoplastic film placed between the loading tip and crown surface. Data was analyzed using ANOVA and Bonferroni post hoc assessment. Fractographic analysis was performed with scanning electron microscopy (SEM).

RESULTS

The mean fracture load (standard deviation) was 1499 (241) N for TD; 1228 (287) N for MD; and 1377 (96) N for ME. Statistically significant difference between groups did not exist (p = 0.157, F = 1.995). In groups TD and MD with low e-modulus abutments, the dispersion of a probability distribution (coefficient of variation: CV) was statistically higher than that of group ME with high e-modulus abutments. SEM illustrated larger micro-fracture dimensions in Group MD than Group ME.

CONCLUSION

Minimal thickness e.max crowns did not demonstrate statistical difference in fracture resistance from traditional thickness crowns. Fracture mechanisms of minimal thickness e.max crowns may be affected by the e-modulus of the substrate. Minimal thickness e.max crowns may be a viable restorative option when supported by high e-modulus materials.

Effect of cavity design on the fracture resistance of zirconia onlay ceramics

Objective

The purpose of this study was to evaluate the fracture resistance and failure modes of onlay restorations prepared with different preparation designs.

Materials and Methods

A total of 42 extracted, mandibular first molars (36, 46) were used and divided into six groups according to preparation design, as follows 1A: Anatomic preparation of cusps/rounded shoulder margin/occlusal groove; 1B: Flat preparation of cusps/rounded shoulder margin/occlusal groove; 2A: Anatomical preparation of cusps/occlusal groove; 2B: Flat preparation of cusps/occlusal groove; 3A: Complete anatomical reduction of cusps/rounded shoulder margin; 3B: Complete flat reduction of cusps/rounded shoulder margin groups; intact tooth: No preparation. Onlays were constructed with 0.5-mm copings of Zirconia ceramic. The copings were veneered with porcelain (IPS e. max Ceram). All samples were subjected to fracture resistance testing. Data were analyzed with Kruskal-Wallis and Bonferroni-Dunn tests.

Results

Fracture resistance varied significantly according to preparation design. Among the anatomic occlusal preparation designs, fracture resistance was significantly lower in Group 3 when compared to Groups 1 and 2 (P < 0.05). Among the flat occlusal preparation designs, fracture resistance was significantly higher in Group 1 when compared to Groups 2 and 3 (P < 0.05).

Conclusion

Preparation design affected the fracture resistance of onlay restorations. Cavities with flat occlusal preparation designs, a groove and shoulder margins (1B) resulted in the highest fracture resistance, whereas teeth prepared with a complete reduction of cusps and shoulder margins (3A) had the lowest fracture resistance.

Influence of preparation design on the quality of tooth preparation in preclinical dental education

Background/purpose

One of the major educational goals in preclinical dental education is to learn tooth preparation techniques. The purpose of this study was to evaluate the influence of different preparation designs on the development of the manual dexterity of students, in order to perform a state-of-the-art tooth preparation.

Material and methods

Seventy-two 1^st semester students were divided into two groups and educated in tooth preparation for a ceramic anterior single crown. One group received cylindrical burs with a rounded edge to prepare a typodont model with a shoulder finishing line, while the other group had cylindrical burs with round noses to prepare a chamfer finishing line. All preparations were digitized and evaluated using special software focusing on the parameters of preparation depth and preparation angle. In addition, violation of the adjacent teeth was estimated. Data was statistically evaluated at a level of significance of 5%.

Results

The preparation design used did not show a statistically significant influence on the preparation depth or on the preparation angle. A trend to a higher tooth structure removal as required was detected. Furthermore, no influence of the type of preparation design on the number of violated adjacent teeth was found.

Conclusion

In preclinical dental education, the type of preparation design was found to have no influence on the measured parameters representing the quality of the preparation.