|Year : 2021 | Volume
| Issue : 4 | Page : 272-276
Comparative evaluation of fracture resistance and mode of failure of ceramic veneers with different design preparations
Nitin Sharma1, Rajeev Gupta2, Archana Nagpal2, Vishal Katna2, Rupandeep Kaur Samra3
1 Department of Oral Health Sciences, Zonal Hospital, Mandi, Himachal Pradesh, India
2 Department of Prosthodontics, Himachal Dental College, Mandi, Himachal Pradesh, India
3 Department of Prosthodontics, Luxmi Bai Institute of Dental Sciences and Hospital, Patiala, Punjab, India
|Date of Web Publication||08-Oct-2021|
Department of Oral Health Sciences, Zonal Hospital, Mandi, Himachal Pradesh
Source of Support: None, Conflict of Interest: None
Background: Ceramic veneers is one of the conservative esthetic treatment modality in dentistry. Success of veneer is very much dependent on the design preparation. Materials and Methods: Thirty selected teeth were categorized within three groups of 10 each with varying design preparations. After mounting the specimens, the incisal reduction was done, and porcelain laminate veneers were fabricated. Then cementation of the veneers was done with resin-cement, and fracture load was applied and recorded. Results: Multiple comparisons were done using post-hoc Tukey's test and modality of failure of veneers among the different designs were done using Chi-square test with the level of significance fixed at 0.05. Conclusion: Ceramic veneers preparation design including1 mm incisal reduction along with 1 mm of palatal-chamfer height revealed greater fracture toughness in contrast to incisal-reduction 1 mm along with butt-joint preparation design.
Keywords: Ceramic veneers, fracture resistance, preparation
|How to cite this article:|
Sharma N, Gupta R, Nagpal A, Katna V, Samra RK. Comparative evaluation of fracture resistance and mode of failure of ceramic veneers with different design preparations. Indian J Dent Sci 2021;13:272-6
|How to cite this URL:|
Sharma N, Gupta R, Nagpal A, Katna V, Samra RK. Comparative evaluation of fracture resistance and mode of failure of ceramic veneers with different design preparations. Indian J Dent Sci [serial online] 2021 [cited 2022 Aug 19];13:272-6. Available from: http://www.ijds.in/text.asp?2021/13/4/272/327806
| Introduction|| |
Veneer is defined as fine layer of tooth-colored restorative material which is applied on a tooth for restoration of generalized or local defects or to enhance the esthetics of patient. Ceramic veneers turned to be most popular treatment modality during the late 1920s and 1930s.
The porcelain veneer is a conservative alternative to complete coverage for improving appearance of an anterior tooth as porcelain is almost ideal in its ability to mimic translucence and structure of natural teeth. Indications for ceramic veneers comprise hypoplasia of enamel, tooth discoloration due to internal staining (tetracycline stains), mutilated teeth, diastema closure, and restoration of malformed teeth., The contraindications include edge-to-edge and anterior cross bite due to overload during function, in patients with excess proclination of anterior teeth, poor dental hygiene, and in case of dentinal demineralization.,,, The technique for veneering requires the shallow reduction of enamel on labial surfaces to approximately 0.5 mm in depth without exposing the underlying dentin as this results in inadequate bonding of the restoration and further the under preparation results in the technical problems in the laboratory fabrication of the restoration as excessive bulk in the gingival part of the restoration can adversely affect emergence profile, resulting in the gingival inflammation.
The Clyde and Gilmour introduced different tooth preparation designs for veneers. Hui et al. introduced feather-edge design of incisal portion with 0.5–1.0 mm bevel placed incisally and intraenamel or “window” preparation of tooth with 1 mm of the incisal edge is maintained.,
The difference of thermal expansion coefficient of tooth from that of resin cement is utilized to bond ceramic veneer with etched enamel surface. This further results in polymerization shrinkage of resin cement, leading to microscopic gap formation which allows the entrance of fluid, debris, and bacteria to penetrate under the margins, resulting in caries and promotion of stain and discoloration. Cement may be washed out by saliva or thermal stress which may weaken the bond between veneer and cement or enamel and cement. The introduction of new ceramic materials, as well as advances in the field of adhesive cementation techniques, has increased the use of ceramic veneers as conservative restorations for anterior teeth.
The aim of this study was to determine and compare resistance to fracture and modality of failures of veneers with different designs of tooth preparations.
| Materials and Methods|| |
This comparative study was conducted to differentiate and assess resistance to fracture and modality of failure of ceramic veneers with various design preparations.
Thirty extracted, maxillary central incisors with approximately 10 mm length of crown, uniformly wide mesiodistally and facio-palatally were chosen for our study. The teeth were examined regarding deformities such as fractures, caries, restorations, and then cleaned and stored in normal saline solution at normal temperature until testing.
They were divided into three groups on the basis of tooth preparation designs:
- Group I: without reduction of incisal edge with facio-incisal bevel
- Group II: 1 mm reduction of incisal edge with butt-joint preparation
- Group III: 1 mm reduction of incisal edge along with preparation of 1 mm chamfer palatally.
Mounting of teeth
Thirty teeth were mounted separately perpendicularly to horizontal plane. The self-cure acrylic material (DPI Rr Cold Cure) (15 mm × 15 mm × 25 mm) was used for mounting the teeth.
Preparation of teeth
The facial surface of tooth was divided into mesial and distal halves. Three depth cuts (0.5 mm) were prepared over the incisal surface facially along the half surface with the help of depth indicating burs (DW-11) (Coltene Diatech crown preparation burs), while other half of facial surface acted as control. The overall trimming of 0.5 mm was performed on other half surface with the help of chamfer end bur (TF-11) (Coltene Diatech crown preparation burs); similarly, the other half of facial surface acting as standard which was later prepared similarly. Self-restricting depth cutting discs 0.5 mm were utilized for defining depth cuts.
Group I: In this group, no incisal reduction was done. Tooth reduction was performed 0.5 mm facio-incisally with 0.2 mm beveling at expense of labial-surface.
Group II: In this group, no incisal reduction was done. 0.5 mm Facio-incisal surface of tooth was trimmed upto 0.5 mm, and incisal finishing line was prepared at 75° inclination towards the lingual surface of tooth with butt joint finishing line preparation.
Group III: In this group, central incisors were reduced upto 1 mm incisally. The chamfer was provided on palatal surface utilizing tapered round end bur, which was placed collaterally with lingual surface of central incisor, resulting in formation of 0.5 mm deep chamfer located 1 mm away from prepared incisal-edges.
Two-step (putty/wash) impression technique with spacer was utilized for making of an impression with cylindrical custom tray and polyvinlysiloxane putty impression material (Coltene Affinis, Impression putty Addition Silicone, Coltene-whaledent). The light-body elastomeric material for impression (Coltene Affinis, light body Addition Silicone, Coltene-whaledent) was inserted in region surrounding designed tooth along with set putty impression.
Master die fabrication
The type IV gypsum (die stone) (Kalrock: Kalabhai Karson Pvt. Ltd) was used for the preparation of the master die [Figure 1].
Fabrication of ceramic veneers
The veneer restorations were designed in the same manner other restorations fabricated from lithium disilicate in wax-up such that these restorations meet the criteria such as strength and esthetic requirements [Figure 1].
Waxing and finishing
The area of tooth preparation was established in a detailed wax-up such that minimal finishing was required [Figure 2]. The wax patterns were removed gently and attached to sprues which were further attached to crucible former. The investment material was then mixed and poured in the casting ring. Then, the burnout procedure was carried out for wax elimination. The invested mold was then filled with lithium disilicate which was pressed in press furnace. The pressed component is placed in weak acid (i.e., e max Invex liquid) for half an hour. To remove the reaction layer this (Emax Ivoclar) component then undergoes sand blasting with100 μm aluminum oxide at 1–2 bar atmospheric pressure while safeguarding the margins. For the cementation of ceramic veneers: Internal surface of veneer was etched using 5% of HF gel up to 20 s and rinsed for 15–20 s. Then, application of silane coupling and bonding-agent was done over ceramic veneer up to 1 min. The prepared tooth was etched with 37% H3PO4 applied up to 15 s and rinsed up to 10 s. Then, application of bonding-agent over teeth was performed and light cured up to 10 s. Dual-cure resin cement (varolink N) base and catalyst were manipulated and applied over veneer which was then placed over the prepared tooth [Figure 3].
Samples were tested in Universal Testing Machine. Teeth with luted veneers was mounted perpendicularly to horizontal plane and the assembly was placed in metal jig. Then application of fracture load at point 1 mm from incisal-edge, perpendicular to the palatal surface was performed [Figure 4]. A prefabricated plunger tip was incorporated to UTM along with the application of load at cross-head speed of 0.5 mm/minute. The values of Fracture-load and modality of failure were noted for each specimen.
|Figure 4: Load application on the tooth at 90 degree to the palatal surface of the tooth|
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| Results|| |
Three groups of teeth were compared for mean fracture resistance utilizing analysis of variance. Multiple comparisons were done using post hoc Tukey test [Table 1]. Comparison of failure modality of veneers and teeth among three groups was done using Chi-square test [Table 2]. Mark of significance for undergoing experiment was fixed at 0.05.
Multiple comparisons in [Table 2] revealed that there was statistically relevant variation in mean fracture resistance of Group I and II (P < 0.05). Statistically relevant difference was revealed in mean fracture resistance of Group I and III (P < 0.05). Mean resistance to fracture of Group III was significantly greater than Group I. No statistically relevant variation was observed in mean fracture resistance of Group II and III (P > 0.05).
| Discussion|| |
Previous studies which were performed to distinguish fracture resistance of various tooth preparation patterns for veneers tested the samples by applying load to tooth-veneer assembly straightly at edge of incisor or along the path perpendicular with central axis of tooth. As orthognathic inter-incisal angle being 135°, stresses that effect maxillary veneers while mastication and protrusive mandibular movements are not normally directed along long-axis of maxillary central incisors.
Ceramic veneers are highly prone for failure on exposure to tensile loads. Thus, in the present study, only horizontal-component of load induced by mandibular-incisors on palatal surface of maxillary-incisors was contemplated when placing samples while checking in a universal testing machine. Thus, veneers were placed perpendicular along the central axis of tooth at 1 mm away from incisal edge. This angle also averted plunger cross head from slipping along the palatal surface of maxillary central incisor.,
From this study, it was observed that average fracture resistance for tooth preparation design with no incisal reduction with facio-incisal bevel was 331.83 ± 14.62 N, for tooth preparation design with 1 mm incisal reduction with butt joint preparation was 488.23 ± 12.05 N and for tooth preparation design with 1 mm incisal reduction along with 1 mm height of palatal chamfer found to be 499.71 ± 8.26 N. Statistically relevant difference in average fracture resistance of tooth preparation design with no incisal reduction with facio-incisal bevel and design of tooth preparation was noted with 1 mm incisal reduction with butt joint preparation (P < 0.05). Average fracture resistance of tooth preparation design with 1 mm incisal reduction with butt joint preparation was markedly greater than that of tooth preparation design with no incisal reduction with facio-incisal bevel. However, statistically relevant difference was observed in that of tooth preparation design with no incisal reduction with facio-incisal bevel and tooth preparation design with 1 mm incisal reduction along with 1 mm height of palatal chamfer (P < 0.05).
The tooth preparation design with no incisal reduction with facio-incisal bevel showed greatest frequency of fractures of ceramic veneers with the value of 55.5% of all the fractures among all three tooth preparation designs. The bond failure and fracture failure modality was recorded highest, i.e., 66.6% in tooth preparation design with no incisal reduction with facio-incisal bevel.
This study revealed that frequency of veneer fracture was least recorded in tooth preparation design with 1 mm incisal reduction along with 1 mm height of palatal chamfer, whereas the frequency of veneer fracture was recorded highest in the tooth preparation design with no incisal reduction along with facio-incisal bevel. The incisal bevel provided in preparation along deign resulted in thin incisal edge which resulted in fracture of the incisal portion of the ceramic veneer whereas butt joint configuration and palatal chamfer configuration provided additional bonding to enamel surface area for the ceramic veneer with greater thickness which resulted in lesser fracture failure modalities in these groups. This investigation is in agreement with study conducted by Magne et al. according to which contraction of luting composite causes stresses at both surfaces and associations of the restoration. In this study, overall preparation was done in enamel, so the tooth preparation design with 1 mm incisal reduction along with 1 mm chamfer placed in palatal position showed greater bonding surface thus resulting in higher fracture resistance values in comparison to the other designs; whereas when dentin is exposed, it resulted in greater chances of microlekage because the chemical bond strength of dentin bonding agent was not sufficient to resist forces of polymerization contraction toward ceramic veneers. The results were in agreement with previous studies carried out by Peumans et al., Ferrari et al., Tijan et al., Prasanth et al., Gruel et al., and Schmidt et al.
Mode of failure of teeth in the present study showed maximum intact teeth, i.e., 66.7% in tooth preparation design with 1 mm incisal reduction along with 1 mm height of palatal chamfer. Maximum frequency of coronal fractures 58.3% were recorded in tooth preparation design with no incisal reduction with facio-incisal bevel, while the cervical fracture occurred with equal frequencies of 40% in both tooth preparation design with no incisal reduction with facio-incisal bevel and tooth preparation design with 1 mm incisal reduction with butt joint preparation. However, the study had certain limitation. The present study was carried out in in vitro conditions; the results may vary in actual oral conditions.
| Conclusion|| |
Within the limitations of present study, following conclusions can be drawn:
- Veneers with 1 mm reduction of incisor edge and with 1 mm height of chamfer placed at palatal position revealed greatest resistance to fracture.
- Veneer with no incisal reduction and bevel placed incisally showed least resistance to fracture in contrast to other tooth preparation designs.
- The tooth preparation design with 1 mm of incisal reduction with 1 mm height of palatal-chamfer is the most stable preparation and yields better results.
Ethical approval was obtained from the ethics committee of the dental institute with reference number HDC/Prostho/Ethical/2015/01.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]