|Year : 2022 | Volume
| Issue : 4 | Page : 361-367
Comparative evaluation of fracture resistance of anterior provisional restorations fabricated using conventional and digital techniques – An in vitro study
Maqbul Alam1, Anshul Chugh1, Adarsh Kumar2, Manu Rathee1, Prachi Jain1
1 Department of Prosthodontics and Crown and Bridge, Post Graduate Institute of Dental Sciences, Rohtak, Haryana, India
2 Department of Public Health Dentistry, Post Graduate Institute of Dental Sciences, Rohtak, Haryana, India
|Date of Submission||15-Dec-2021|
|Date of Decision||25-May-2022|
|Date of Acceptance||29-May-2022|
|Date of Web Publication||03-Oct-2022|
Associate Professor, Department of Prosthodontics and Crown and Bridge, Post Graduate Institute of Dental Sciences, Rohtak - 124 001, Haryana
Source of Support: None, Conflict of Interest: None
Aim: Comparative evaluation of the fracture resistance of anterior provisional crowns fabricated by conventional and digital techniques.
Settings and Design: Department of Prosthodontic, PGIDS, Rohtak, An in-vitro – Comparative study.
Materials and Methods: Thirty recently extracted maxillary central incisors were handpicked. Tooth preparation was done according to the principles of tooth preparation. A single-step impression technique was used for impression making of the prepared tooth and stone models were poured. Extracted teeth were divided into 3 groups (n = 10 each) based on provisional crown fabrication technique. A bis-acryl-based (Protemp 4 3M ESPE) resin was used to fabricate the provisional crowns by the conventional indirect technique. The rest of the stone models (20) were scanned using lab scanner (Dentsply Sirona InLab EOS X5). CAD/CAM provisional material (Dentsply Sirona multilayer PolyMethyl Methacrylate) PMMA disc was used for fabrication of provisional restoration through milling technique. 3D printed temporary provisional material (NextDent C&B resin) was utilized for 3D printed provisional crowns. Cementation of provisional crowns was done using eugenol free temporary luting cement (Templute, Prime dental). All cemented provisional crowns were subjected to load under Universal Testing Machine. The maximum load to produce fracture for each specimen was recorded in Newton (N).
Statistical Analysis Used: Shapiro–Wilk test was employed to test the normality of data. Kruskal- Wallis Test was used to compare the mean fracture resistance between all the groups. For intergroup comparison Mann-Whitney U Test was used.
Results: The mean fracture resistance of group I (Conventional technique) was found to be 558.8459700 ± 22.33 N; for group II (CAD/CAM technique) 960.8427200 ± 37.49 N and for group III (3D Printed technique) 1243.1774000 ± 68.18 N. Group I had the least fracture resistance value while group III showed maximum value.
Conclusion: Provisional crowns fabricated using 3-D printing technique showed higher fracture resistance followed by CAD/CAM technique and conventional technique. Additive manufacturing of provisional crowns using 3-D printing technique could be considered a reliable and conservative method for the fabrication of stronger provisional restorations.
Keywords: Computer-aided design and computer/aided manufacturing technology, fracture resistance, provisional restoration, three-dimensional printing
|How to cite this article:|
Alam M, Chugh A, Kumar A, Rathee M, Jain P. Comparative evaluation of fracture resistance of anterior provisional restorations fabricated using conventional and digital techniques – An in vitro study. J Indian Prosthodont Soc 2022;22:361-7
|How to cite this URL:|
Alam M, Chugh A, Kumar A, Rathee M, Jain P. Comparative evaluation of fracture resistance of anterior provisional restorations fabricated using conventional and digital techniques – An in vitro study. J Indian Prosthodont Soc [serial online] 2022 [cited 2022 Dec 7];22:361-7. Available from: https://www.j-ips.org/text.asp?2022/22/4/361/357803
| Introduction|| |
One of the most significant components of provisional, temporary, or interim restorations is meeting the patient's functional and aesthetic demands. They are of great significance, especially in those cases where longer duration of treatment is needed before delivery of the final prosthesis.,
According to Shillingburg, a provisional restoration should provide pulp protection of underlying prepared tooth from the external and internal noxious stimuli, protect periodontium, prevent supra eruption or mesial or distal tipping of tooth, and should be in harmonious occlusion and easy hygienic maintenance. They should be esthetically pleasing, biocompatible with the surrounding tissues such as the gingiva, should maintain the gingival health as well as emergence profile and should not induce any gingival pathosis. Proper marginal adaptation, low thermal conductivity, mechanical properties such as fracture resistance, strength, and wear resistance are the indispensable requirements of provisional restorations.
One of the most common causes attributed to a failure of provisional restorations is the fracture of the prosthesis causing patient discomfort and economic loss. Fracture resistance is a mechanical property that describes the resistance of brittle materials to the catastrophic propagation of flaws under applied stress.
The provisional restoration can be fabricated using the conventional chair-side method, in the laboratory on working casts, or more recently by the use of digital technology. Conventional technique fabrication includes prefabricated versus custom made which are further classified into direct, indirect, and direct-indirect methods. It has many disadvantages such as the production of exothermic heat, high residual monomer content, and more shrinkage resulting in dimensional discrepancies. It also affects the mechanical properties and fit of the prosthesis.
Computer-aided design and computer-aided manufacturing system (CAD/CAM) have been introduced to simplify the method and eliminate the common errors associated with the conventional provisional technique; however, it has its own flaws.
Recently, introduced additive system, i.e., three-dimensional (3D) printing system has superior qualities in the fabrication of provisional restorations, to overcome the demerits of previous techniques. Many studies have been done in the past comparing the provisional crown fabricated by conventional method and those fabricated using CAD/CAM milling technique on posterior teeth but lacks on anterior teeth, which are of utmost importance in esthetic zone.,
Therefore, this study aimed to compare the fracture resistance of anterior provisional crowns fabricated by conventional techniques and those fabricated by digital techniques.
| Materials and Methods|| |
Thirty extracted maxillary central incisors of approximate anatomic crown length and mesiodistal dimensions were selected.
All the specimens were mounted in self-polymerizing acrylic resin using customized mounting mold and keeping the long axis parallel to mold using Ney surveyor. Specimens were divided into three groups of 10 each as follows:
- Group I: Provisional crown fabricated using conventional technique
- Group II: Provisional crown fabricated using CAD/CAM milling technique
- Group III: Provisional crown fabricated using 3D printed technique.
Preparation of the specimens
A tooth preparation kit (Shofu crown and bridge tooth preparation kit, India) was used for tooth preparation. It was done according to the principles of tooth preparation. Specimens were prepared for all ceramic full coverage crowns with shoulder finish line.
To make the impression of the prepared tooth, a metal custom tray with perforations was made. The tray had similar dimensions to that of the acrylic block for accurate seating on the block. The tray had a space of 6 mm for the impression material. Polyvinylsiloxane impression material (AVEUTM gum putty, Made in Korea) was loaded in the custom tray and light body impression material (AVEUTM light body, Made in Korea) was loaded on the prepared tooth and single step impression was made. The loaded tray with putty impression material was placed on the acrylic block and a single-step impression was made. All the impressions were then poured in die stone (Ultra rock brown die stone; Kalabhai Karson Pvt. Ltd.) with the help of vibrator to avoid any void or bubble formation.
Fabrication of provisional crowns
Fabrication of provisional crowns by conventional method (Group I)
Before the commencement of tooth preparation, a putty index of the unprepared mounted tooth was made. Following the preparation of the mounted tooth, its impression was made using putty and light body impression material. Impression was poured using a vibrator and a die stone model was obtained. Cement space thickness was defined at 30 μm by applying the die spacer of the same thickness. Provisional restoration material Protemp4 TM was dispensed through dispensing tip into the preformed putty index, and thereafter, the index was seated over the stone model. For the exact seating of putty index onto the stone model, parallel vertical lines were scribed onto the stone model as well as in the putty index. Excess of provisional restoration material was removed using explorer and finishing and polishing of provisional restoration were done using acrylic finishing and polishing kit.
Fabrication of provisional crowns by milling technique (Group II)
The stone model was scanned with the help of a scanner (Dentsply Sirona In early-onset scoliosis [EOS] X5) [Figure 1]a. Surface tessellation language (STL) file of the scanned model was obtained [Figure 1]b. Designing of provisional crowns was done using EXOCAD software and. STL files of the provisional crowns were created [Figure 1]c. Cement space thickness was defined at 30 μm. Polymethyl methacrylate (PMMA) CAD disc was selected. Virtual sprue attachment was done. The. STL file of the designed data was fed into the milling machine (DentsplySironaInLab MC X5). Wet milling of the PMMA disc was performed [Figure 1d]. Later, sprue was removed from the milled disk. Finishing and polishing of the crowns were performed using an acrylic finishing and polishing kit.
|Figure 1: (a) Scanning of the stone die, (b) STL file of scanned stone die, (c) Designing of provisional crowns, (d) Milled provisional crowns, STL: Surface tessellation language|
Click here to view
Fabrication of provisional crowns by 3D printing (Group III)
The stone model was scanned with the help of a scanner (Dentsply Sirona In EOS X5) to generate a. STL file. The provisional restoration was designed using the EXOCAD software program. Cement space thickness was defined at 30 μm and the thickness of the build layer was kept at 0.05 mm. NextDent C and B resin was activated using an LC-3DM mixer [Figure 2]a. After activation, the resin was poured into a 3D printer container in the NextDent 5100 printer. The. STL file was generated and data fed to the NextDent 5100 printer [Figure 2]b. Objects were built layer-by-layer. The ultraviolet light (405 nm) cured each layer and hardened a thin layer of the polymer. The process continued until the completion of the full object with the layer thickness of about 50 μm with supporting structures [Figure 2]c. The printing cycle took about 30 min for partial curing of each provisional crown.
|Figure 2: (a) Activation of NextDent C and B resin, (b) Orientation of provisional crown STL files on printing table, (c) 3D Printed crowns, (d) Post curing of 3D printed crown, 3D: Three-dimensional|
Click here to view
Postprocessing and curing of 3D printed provisional restoration was done. Supporting structures were removed. To remove and clean the uncured resin, printed crowns were cleaned with 96% isopropyl alcohol. The NextDent LC-3DPrint Box (wavelength 350–550 nm) was used for 30 min for postcuring of 3D printed resin materials to ensure that materials achieve full polymerization [Figure 2]d.
Cementation of provisional crown
Finished and polished provisional restorations were evaluated for any voids, bubbles on the inner surface of the crown and any marginal inadequacy. TempluteTM (Prime Dental Products, India) noneugenol-based temporary luting cement was used for cementation. The entire inner surface of the provisional crown was coated with the mixed cement and the crown was placed on the prepared tooth with finger pressure to maintain constant pressure. After the initial set, excess cement was removed using explorer.
Mechanical testing of the specimens
A customized metal jig was fabricated to hold the specimen at 135° to the long axis of the tooth under universal testing machine. Fracture resistance tests of the specimens were performed using a universal testing machine (UNITEK 94100). Cemented specimens from all the Groups (I, II, and III) were loaded at 135° degrees to the long axis of the tooth simulating load during intercuspal movements. The load was applied 3 mm below the incisal edge on the center of the palatal surface of the cemented provisional crowns with a load applicator attached to the upper movable compartment of the machine with a crosshead speed of 1.0 mm/min [Figure 3]. Each specimen's maximal load to cause fracture was measured in Newton.
|Figure 3: (a) Testing of specimen under Universal Testing Machine, (b) Fracture crown after testing|
Click here to view
Data obtained were checked for normality using the Shapiro–Wilk test and it was found that the data followed a nonnormal curve; hence, nonparametric tests have been used for comparisons. Kruskal–Wallis test was used to compare the mean fracture resistance between all the groups. For intergroup comparison, Mann–Whitney U-test was used.
| Results|| |
Descriptive statistics showed mean values, median and standard deviation of the effect of three techniques (Conventional technique versus CAD/CAM technique versus 3D printed technique) tabulated in [Table 1] and drawn in the [Graph 1].
|Table 1: Mean value and standard deviation and median of Groups I, II, and III|
Click here to view
The mean of Group I (provisional crown fabricated by conventional technique) was 558.84597 ± 22.33, whereas for Group II (Provisional crown fabricated by CAD/CAM milling technique) 960.84272 ± 37.49 and Group III (Provisional crown fabricated by CAD/CAM milling technique) was 1243.17740 ± 68.18. Group III showed the maximum mean fracture resistance of 1243.17N amongst all; whilst Group I showed the least fracture resistance of 558.84N. Statistically significant results and significant difference in mean fracture strength were found.
| Discussion|| |
Provisionalization is an integral step in the treatment of fixed prostheses. Provisionalization's biological, mechanical, and esthetic criteria must be considered for success during the temporization phase of treatment. Various provisional materials have evolved over time regarding biologic, mechanical, and esthetic properties, which make them suitable in the specific area. The interim restoration is employed in-between from the time of tooth preparation till final cementation is done. To ensure a successful final restoration, a suitable fabricated provisional restoration is important, which becomes even more crucial in cases of full mouth rehabilitations. Provisional restorations are often utilized for relatively long periods (6–12 weeks) to monitor patient comfort and satisfaction.
Provisional restorations are fabricated using a variety of techniques. The manual technique is further classified into direct, indirect, and indirect-direct techniques. Advancements in materials and technology aided the development of the CAD/CAM technique, which is further classified into additive and subtractive techniques. The subtractive technique is currently widely used in most modern dentistry facilities i.e., CAD/CAM. Due to ever-changing concepts and technology, we can now print the complex structure by additive technology as well, i.e., 3D printing, which is a quickly gaining attraction, employing a variety of resins. It is capable of simulating exact prostheses with minimal wastage of materials. It is said to be less expensive and faster than milling. Stereolithography, digital light processing, selective laser sintering, and fused deposition modeling are some of the 3D printing techniques.,,
An important requisite of the provisional restoration is that it should not deform under mechanical forces such as masticatory and parafunctional forces. Even though restorations are being planned to avoid failure, still fractures do happen, causing discomfort and financial loss to the patients. To ensure the clinical success, the mechanical strength attributes of provisional materials are critical and should be considered. Restoration fractures during function can be caused by various factors such as incorrect occlusion, bruxism, under contoured pontics, and trauma.,
There are confined studies that correlates and emphasize the mechanical properties such as fracture resistance of provisional restorations. The documented information is mainly available on marginal fit, fracture resistance; build layer effect done on the posterior tooth, but lacks on anterior tooth, which being in esthetic zone cannot be ignored. Therefore, the current research work was done to assess the fracture resistance of anterior provisional restoration fabricated by conventional and digital technologies.
This study was conducted on recently extracted human maxillary central incisors for the advantage such as similar modulus of elasticity, hardness, and strength as teeth present in the oral environment. The selection of extracted maxillary central incisor, vertical mounting of the tooth into self-cure acrylic resin using Ney surveyor was done according to standardization as stated by Stappert et al.,
Group I versus Group II, (conventional technique versus CAD/CAM technique) showed that there was a statistically highly significant difference seen for the values between the Groups I versus II (P < 0.01) with higher values for Group II as compared to Group I. This result coincides with the finding of research conducted by Reeponmaha et al., Rayyan et al. and Abdullah et al. Reeponmaha et al. conducted a study to evaluate the fracture strength and fracture patterns of provisional crowns fabricated from different materials and techniques after receiving stress from a simulated oral condition. They concluded that provisional restoration fabricated using CAD/CAM techniques showed higher fracture resistance compared to conventionally fabricated monomethylacrylate resin. Rayyan et al. conducted a study with the purpose to compare the color stability, water sorption, wear resistance, surface hardness, fracture resistance, and microleakage of CAD/CAM fabricated interim restorations with that of conventionally fabricated interim restorations. They concluded that CAD/CAM interim crowns showed better physical and mechanical properties than conventional or manually fabricated and may be used for long-term interim restorations. Abdullah et al. did a study to compare the marginal gap, internal fit; fracture strength of CAD/CAM fabricated provisional restoration and concluded that CAD/CAM fabricated provisional crowns demonstrated superior mechanical properties than directly fabricated provisional restoration.
Group I versus Group III, conventional technique versus 3D printed showed that there was a statistically highly significant difference seen for the values between the Groups I versus III (P < 0.01) with higher values for Group III as compared to Group I. The result coincides with the finding of a study done by Tahayeri et al. They evaluated the mechanical properties of 3D printed versus conventionally cured provisional material. Mechanical properties of 3D printed provisional restoration were found to be higher than that of the conventionally fabricated restorations.
Group II versus Group III showed that there was a statistically highly significant difference seen for the values between the Groups III versus II (P < 0.01) with higher values for Group III as compared to Group II. The result coincides with the study done by Joshi et al. and Ibrahim et al. Joshi et al. performed the study to compare the physical and optical properties of provisional crown and bridge materials fabricated using CAD/CAM or 3D printing technology and concluded that milled PMMA has superior flexural strength and hardness compared to 3D printed resins. Ibrahim et al. assessed the fracture resistance of interim restorations fabricated by 3D printing technique and milling technique. They concluded that interim crowns fabricated using the 3D printing technique showed higher fracture resistance compared to milled interim crowns under thermo mechanical loading.,
Based on the results of the present study, superior fracture resistance of Group III can be due to the following reasons:
- The superior fracture resistance could be due to the layered nature of the 3D-printed structure and because of the chemical bonding between the layers. The increased values of the fracture resistance could also be due to the vertical building orientation of the 3D printed interim crowns employed in the present study and higher than horizontally printed specimen with layers parallel to load direction
- The higher fracture resistance could be attributed to the thin printed layer thickness used (50 μm) during the building process. The layer thickness could be an important contributor to the mechanical properties of samples. Lower the layer thickness, the more the layer to layer interfaces available; the better the degree of polymerization for each layer and the more mechanical performance is affected positively
- It could be attributed to the postcuring process of 3D printed crowns that was carried out in a special NextDent curing unit. The use of a postcuring technique on 3D printed crowns can improve fracture toughness and strength by increasing conversion and reducing the presence of residual monomers.
The surface characteristic, topography of provisional not only affect the mechanical properties but also affects the color stability of provisional restorations. Song et al. compared the color stability of provisional restorative materials fabricated by 3D printing, dental milling, and conventional materials and concluded that all the three materials showed varied degree of discoloration with time. All the three materials showed initial excellent colour stability, but there was exponential or more rapid change in color after 8 weeks. Coutinho et al. conducted a study on LuxaCrown, Protemp4, Heat cure PMMA to evaluate color stability of these three materials. They concluded that least color change was observed in heat cure PMMA followed by Protemp4 and highest difference was seen in LuxaCrown.
The present study was novel as three provisional restoration materials selected were recent ones. The previous studies were done using the cast of die specimens and were mainly on the posterior tooth while the present study focused on anterior tooth region.
With in the limitations, the merits of this in vitro study were
Based on this study, clinical recommendations can be made that 3D printed restorations are more durable than the other two techniques. This study utilized extracted maxillary central incisors, which simulated the elasticity and other factors of natural teeth.
The present study compares the conventional technique to that of additive and subtractive manufacturing techniques, which has not been done previously to the best of our knowledge.
The present study includes postprocessing parameters of 3D printed crowns, which is an important parameter. Most of the studies regarding marginal fit comparison, internal fit comparison and fracture resistance and fracture pattern have been done mostly on posterior tooth whereas the present study compares of provisional restoration of anterior tooth region.
The limitations of the study are as follows
Extracted human maxillary incisors used had the disadvantage of variations in age and quality, thus compromising on the standardization of the bonded interface of cement and tooth. The periodontal ligament considerations were not taken into account. Acrylic resin was employed to embed the teeth, which had a different biomechanical position than the oral cavity and did not mimic the clinical situation.
The restoration was cemented with finger pressure, which is clinically applicable. The failure load was employed to assess the restoration's resistance alone, although in the oral environment, a variety of variables are present. Additional elements, including the physical and chemical stresses that the repair are exposed to over a long period of time in the clinic, may have an impact on the outcome.
Thermal variations are known to cause cracking and failure of the provisional restorations clinically. The cement used for luting the provisional crowns may impose surface changes on the crowns when it is subjected to thermal variations. Thermocycling with variable temperatures was not used in this investigation, which could have influenced the fracture resistance rating. The fracture patterns of the provisional crowns were not evaluated.
As a result, future research should evaluate the influence of the above-mentioned characteristics, as they may change the fracture resistance values and failure modality of the specimens. The use of artificial periodontal membrane to simulate the clinical condition could improve the research results further. Abutment mobility is a decisive clinical factor for the evaluation of failure load.
| Conclusion|| |
Within the limitations of this in vitro study, it can be concluded that:
- Provisional crowns constructed using 3D printing technique showed higher fracture resistance followed by CAD/CAM technique and conventional technique
- Additive manufacturing of provisional crowns using 3D printing technique could be considered a reliable and conservative method for the production of stronger provisional restorations
- Fracture resistance of all the groups showed clinically acceptable values under mechanical loading.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]