|Year : 2014 | Volume
| Issue : 2 | Page : 71-78
Comparative study of marginal adaptation and mechanical properties of CAD/CAM versus dual polymerized interim fixed dental prosthesis
Marwa Eltayeb I Elagra1, Yousria Shalaby2, Moustafa Fakhry Khalil3, Nagiub ElFawal2
1 Department of Prosthodontics, Faculty of Dentistry, Riyadh Colleges of Dentistry and Pharmacy, Riyadh, Kingdom of Saudi Arabia
2 Department of Conservative Dentistry, Faculty of Dentistry, University of Alexandria, Alexandria, Egypt
3 Department of Biomaterials, Faculty of Dentistry, University of Alexandria, Alexandria, Egypt
|Date of Web Publication||12-Aug-2014|
Dr. Marwa Eltayeb I Elagra
Riyadh Colleges of Dentistry and Pharmacy, Riyadh
Kingdom of Saudi Arabia
Source of Support: None, Conflict of Interest: None
Background: With the advent of new interim crown materials, it has become imperative to evaluate its strength in order to select the appropriate interim crown and partial fixed dental prosthesis material.
Aim: The purpose of this in vitro study was to compare marginal adaptation, wear resistance, and fracture resistance of a computer-aided design/computer-aided manufacturing (CAD/CAM) versus a dual polymerized interim fixed dental prosthesis (FDP).
Materials and Methods: Twenty models were randomly allocated into two equal groups (I and II). Group (I) received 10 CAD/CAM fabricated interim FDP (CAD-Temp) and Group (II) received 10 directly fabricated interim FDP using a dual polymerized material (TempSpan). All specimens were stored before testing. Marginal adaptation was tested using stereomicroscope and image analyzing software to measure the amount of marginal gap. For wear resistance test, all specimens were subjected to mechanical tooth brushing. Stereomicroscope and image analyzing software were used to measure the difference in height before and after tooth brushing. Specimens were subjected to cyclic loading; specimens intact from defects were then loaded to fracture. Data were analyzed using Student's T- test, Mann Whitney test and Fisher exact test (α = 0.05).
Results: CAD-Temp (15.026 ± 4.340 μm) showed significantly higher marginal adaptation than TempSpan (145.418 ± 25.365μm)(P < 0.001). The wear resistance of CAD-Temp (7.3322 ± 0.99853 μm) was significantly higher than TempSpan (22.3165 ± 2.35459 μm) (P < 0.001). The fracture resistance of CAD-Temp (605.1 ± 31.718N) was also significantly higher than that of TempSpan (225.76 ± 32.469N) (P < 0.001).
Conclusions: CAD/CAM fabricated interim restorations have better marginal adaptation, wear resistance and fracture resistance than dual polymerized interim restorations hence, might withstand longer duration in the oral cavity.
Keywords: CAD/CAM, dual polymerized material, Interim FDP
|How to cite this article:|
Elagra MI, Shalaby Y, Khalil MF, ElFawal N. Comparative study of marginal adaptation and mechanical properties of CAD/CAM versus dual polymerized interim fixed dental prosthesis. Saudi J Oral Sci 2014;1:71-8
|How to cite this URL:|
Elagra MI, Shalaby Y, Khalil MF, ElFawal N. Comparative study of marginal adaptation and mechanical properties of CAD/CAM versus dual polymerized interim fixed dental prosthesis. Saudi J Oral Sci [serial online] 2014 [cited 2019 Dec 15];1:71-8. Available from: http://www.saudijos.org/text.asp?2014/1/2/71/138467
| Introduction|| |
A provisional restoration functions as an interim restoration from the time the tooth area is prepared for restorative procedures until the final prosthesis is cemented in place in the mouth.  While the terms provisional, interim, or transitional restoration have been routinely used interchangeably in the literature, the use of the term temporary is controversial and is considered inappropriate by some because interim restorations serve many functions, and "temporary" treatment may be interpreted as one of lesser importance or value. ,, The objectives of provisionally restoring prepared abutment teeth are to provide protection, positional stability, masticatory ability, and esthetics, as well as to obtain certain diagnostic information.  To ensure these objectives are achieved, the material used to fabricate the interim prosthesis ideally should have a low polymerization shrinkage so as to satisfy biologic and esthetic needs as well as mechanical requirements, such as resistance to functional loads. 
Long-term dimensional stability of the interim restoration in the oral environment is an important consideration for complex integrated treatment plans where the final restoration is delayed until completion of periodontal, endodontic, and orthodontic therapy. ,,,
The computer-aided design/computer-aided manufacturing (CAD/CAM) technology offers the possibility to produce dental restorations by means of numeric controlled machining.  The many benefits associated with CAD/CAM-generated dental restorations include: the access to new, almost defect-free, industrially prefabricated, and controlled materials; an increase in quality and reproducibility and also data storage commensurate with a standardized chain of production; an improvement in precision and planning, as well as an increase in efficiency.  CAD/CAM technology can be employed for the fabrication of permanent restorations, as well as temporary restorations to be milled from industrially produced blocks. , Most of these blocks as claimed by their manufacturer data are made of cross-linked polymethylmethacrylate (PMMA) blocks for the fabrication of long-term temporaries. ,
Traditionally provisional restorations were fabricated using either PMMA or bisphenol a glycidylmethacylate (Bis_GMA), and there is literature available on the relative strengths and abrasion resistance of these materials. ,,,, With the advent of new interim materials, it has become necessary to evaluate their strength in order to select the appropriate interim crown and fixed dental prosthesis (FDP) material. The purpose of this in vitro study was to compare the marginal adaptation, wear resistance, and fracture resistance of interim prostheses prepared using CAD/CAM versus one prepared using a dual polymerized interim fixed dental prosthesis.
| Materials and Methods|| |
The study used CAD/CAM blocks (Temp Blocks (CT- 40); VITA-Zahnfabrik; Germany) and a dual polymerized material (TempSpan; Pentron Clinical Technologies, USA).
Master die was prepared on a student model with interchangeable hard resin teeth: lower right first premolar (#44) and first molar (#46) were prepared for ceramometal crown design.
Three points were engraved by a cutting disk below the facial, lingual, and proximal (mesial of premolar and distal of molar) finish line of the prepared molar and premolar. These points acted as standard reference points. The lower right second premolar (#45) was removed and the socket was blocked and shaped by wax to resemble an edentulous space. A reusable mold of the prepared segment was made from addition cure duplicating silicon. Twenty replicas of the right segment of the model carrying the prepared molar and premolar were made, from metal filled epoxy resin, by the manufacturer. The constructed specimens were then randomly divided into two groups of ten specimens each according to the interim material used.
Production of interim FDP
Preparation of interim FDP using CAD-Temp (Group I)
0CEREC MC XL systems (Sirona dental system; USA) with Sirona's 3D (V 3.01) software was used to design and mill 10 interim FDP made from CAD-Temp blocks. Optical impression for each specimen was captured. CEREC 3D software then transformed the optical data for each preparation into an accurate three-dimensional digital model. A fully anatomical three unit interim FDP restoration design using the 3D software was done. Finally, 10 CAD-Temp blocks were clamped in milling chamber of CEREC 3 machine (Sirona dental system) and milled successively. After milling (CAM), the lug was cut off using a fine cross-cut tungsten carbide bur. The interim FDPs were polished with a silicone polisher and a small goat-hair brush according to the manufacturer instructions and seated on their respective models.
Preparation of interim FDP using TempSpan (Group II)
Negative reproductions of the milled interim FDP was obtained with a silicon rubber base impression material (Virtual; Ivoclarvivadent; Schaan, Germany) held in a quadrant tray. The silicon molds were used to make ten standardized interim FDPs according to the manufacturer instructions.
Crowns with internal or external voids, visible cracks and those that did not adapt to the die on all surfaces were excluded from the study.
The specimens were stored in water for 72 hours before testing because the greatest change of mechanical properties takes place in the first 2-3 days after fabrication of the provisional restorations. 
Testing marginal adaptation
Crowns were tested for marginal adaptation using stereomicroscope (Olympus SZ_CTV; Japan) at 40x magnification. The specimens were measured pre-cementation. The interim FDPs were fixed to the models by a fabricated clamp during the readings under the stereomicroscope. The specimens were placed under the microscope and photographed using a camera that was connected to the microscope. The images were then transferred to image analysis software program (Cell*A imaging solution for life science microscopy; Germany) that measures the vertical marginal gap, from the six reference points at the edge of the chamfer finish line of the dies to the inferior edge of the interim FDPs. To avoid inter-observer error the same well-trained operator did the measurement each time and for all the specimens. The results from each reference point were compiled and the average of six surfaces was calculated for each specimen. Finally, an overall average of marginal gap formation was calculated for each test group. ,,
Testing wear resistance
Using a sharp blade, a horizontal line was engraved on the FDPs, few millimeters away from the tips of the cusps, buccally and lingually. This horizontal line acted as a fixed measuring point. Under the stereomicroscope,  the vertical distance  between cusp tips of the interim FDP, and the horizontal line was measured and tabulated. The amount of wear of each interim FDP was measured at six reference points.th
After the above-mentioned measurements, all specimens were subjected to mechanical brushing using custom made toothbrush abrasion machine (Dental Biomaterial Department; Alexandria University; Alexandria, Egypt) to accomplish brushing action as close as possible to that occurring in the oral cavity. ,,
A new brush (Oral B Procter and Gamble; Weybridge, UK) was used for every specimen. The experimental units were aligned so that the brushing head moved parallel to their occlusal surface. A current dentifrice containing abrasives of aluminum hydroxide (Colgate Fluor guard Colgate-Palmolive; UEGE, Italy) was used as abrasive slurry with a paste-to-water ratio of 1:1. A vertical load of 350 g  on the top of each brush, during horizontal movement was applied on each specimen throughout the test, to ensure equal loading between the brushes and the specimens. After testing, specimens were removed from the machine, rinsed with tap water, cleaned in distilled water for 5 minutes, and gently air dried.
The vertical distance between the cusp tip and the horizontal line was measured again under the stereomicroscope after the mechanical brushing. The amount of wear was the difference between the vertical distance before and after brushing.
The vertical difference from each cusp was compiled and the average of the six cusps was calculated for each specimen. Finally, an overall average of vertical loss formation was calculated for each test group.
All the 20 interim FDPs were cemented on their respective dies using temporary eugenol-free luting cement (Provilat; Promedica; Neumünster, Germany). All the procedures were carried out according to the manufacturer's recommendations and by the same operator.
Cyclic loading and fracture resistance
The cyclic loading was performed using a custom made load cycling machine (Dental Biomaterial Department; Alexandria University).  Cyclic loads in this study corresponded to 3 months of clinical service. , Accordingly, samples were exposed to 60,000 mechanical cycles [Figure 1].
The specimens were examined stereomicroscopically to evaluate the nature of failure if failure occurred.
Specimens that failed during cyclic loading were excluded and only those that were intact from each group were subjected to fracture test.
The interim FDPs specimens were loaded using a Universal mechanical testing machine (Maxi-torq; Comten-industries, inc; Florida, USA). 
Statistical analysis was performed using statistical package for social sciences program Statistical Package for the Social Sciences (SPSS 17.01) software. The study included descriptive and analytical data. A P value <0.05 was considered statistically significant.
Data were presented as means and standard error (SE) values. Results of marginal adaptation and fracture resistance were analyzed using Student's T-test. The results of wear resistance were analyzed using Mann-Whitney test for comparison between unpaired signed ranks test. Fisher exact test was used to analyze and compare the defects that happened following cyclic loading.
| Results|| |
The group vertical gap mean value and the standard error of both Group I (CAD-Temp) and Group II (Tempspan) are listed in [Table 1]. The mean gap difference of the two groups was compared using Student's T-test. TempSpan showed significantly higher mean gap than CAD-Temp; P < 0.001 [Figure 2] and [Figure 3].
|Figure 2: Marginal adaptation results. Group I (CAD-Temp)® (a) a specimen with perfect marginal adaptation, (b) a specimen with marginal discrepancy|
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|Figure 3: Marginal adaptation results Group II (TempSpan)® (a) a specimen with perfect marginal adaptation, (b) a specimen with marginal discrepancy|
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The group wear mean value and the standard error of both CAD-Temp and Tempspan are listed in [Table 2]. The wear mean difference of the two groups was compared using Mann-Whitney test (U test), for comparison between unpaired signed ranks test. CAD-Temp showed significantly higher wear resistance than TempSpan; P < 0.001 [Figure 4] and [Figure 5].
|Figure 4: Wear results. Group I CAD-Temp® (a) Before mechanical tooth-brushing, and (b) After mechanical tooth-brushing|
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|Figure 5: Wear results Group II TempSpan® (a) Before mechanical tooth-brushing and; (b) after mechanical tooth-brushing.|
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|Table 2: Mann-Whitney (U) test statistics comparing mean wear of Group I and Group II; before and after mechanical tooth brushing|
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The number of defects and the mode of failure that happened for both groups following cyclic loading are listed in [Table 3]. Fisher exact test was used to compare the difference in defective specimens between the two groups. There was no statistically significant difference between the two groups in number of defective specimens. P = 0.350 [Table 4], [Figure 6] and [Figure 7].
|Figure 6: Cyclic loading results. (a) CAD-Temp® specimen with marginal chipping after cyclic loading. (b) CAD-Temp® specimen with crack after cyclic loading. (c) TempSpan® specimen with fracture after cyclic loading. (d) TempSpan® specimen with marginal chipping after cyclic loading|
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|Figure 7: A graph illustrating the number of specimens with defects against those with no defect ater cyclic loading in Group I and Group II|
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|Table 3: Number of defects and mode of failure that happened for both groups|
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|Table 4: Fisher exact test statistics comparing groups, in number of defects before and after cyclic loading|
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The group fracture load mean and standard error of both CAD-Temp and TempSpan are listed in [Table 5]. Student's T-test was used to compare the fracture load mean between the two groups. CAD-Temp showed significantly higher fracture resistance than TempSpan P < 0.001 [Figure 8].
|Figure 8: Fracture resistance results. (a) CAD-Temp®: A specimen after fracture. (b) TempSpan®: A specimen after fracture|
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|Table 5: Comparison of fracture resistance (N): Group I versus Group II. (t- test)|
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| Discussion|| |
Due to the continued growth of the implant market, the demand for interim crown and FDP materials for implant cases has been constantly rising. This applies mainly to materials suitable for the fabrication of long-term temporaries. Evaluation of the mechanical properties of interim fixed dental prosthesis materials is important to prevent failure of a temporary restoration from the beginning, after fabrication and insertion.  Therefore, this in vitro study compared the marginal adaptation, wear resistance, load bearing capacity, and fracture strength and Group I (CAD-Temp) CAD/CAM provisional block versus Group II (TempSpan) dual-polymerized interim material.
In this study, the null hypothesis that there was no difference in marginal adaptation, wear resistance, and fracture resistance between CAD/CAM and dual polymerized interim fixed dental prosthesis can be rejected.
Interim fixed dental prosthesis fabricated from TempSpan, dual polymerized interim material, showed significantly higher marginal discrepancy than those fabricated from CAD-Temp, the CAD/CAM provisional blocks; P < 0.001.
The vertical gap mean value of CAD-Temp was 15.026 ± 4.340 μm. The low mean gap exhibited by CAD-Temp might be because the CAD/CAM blocks material as claimed by the manufacturer had homogeneity, high-molecular and cross-linked acrylate polymer with microparticle filler.  It might also be because they were previously industrially polymerized under optimized conditions hence no further polymerization shrinkage is expected to happen. The vertical mean gap value of Tempspan was 145.418 ± 25.365 μm. This high value may be due to the polymerization shrinkage exhibited by the material. Kim and Watts  mentioned that the net magnitude of polymerization shrinkage strain depends upon number of factors, such as the type of monomer, the amount of monomer, the volume fraction of filler particles, filler size, the degree of conversion, the nature of the resin, stiffness and flow of resin, the rate of polymerization, curing characteristics, water sorption, and the intensity of the light used to polymerize the resin. This increased marginal discrepancy demonstrated was in agreement with Givens et al. who tested the marginal adaptation of a dual polymerized material and reported that there was high marginal discrepancy of the dual polymerized material (319 μm). They suggested that the majority of gap formations occurred during the auto-polymerization phase of polymerization of dual polymerized material.
When comparing wear resistance of the two groups, interim FDP fabricated from CAD-Temp had statistically significant higher wear resistance than those of TempSpan; P < 0.001. Although toothbrush abrasion testing is influenced by factors such as the type of testing device, loading, number of strokes, toothbrush type, and dentifrice type,  these parameters were standardized for both groups for better evaluation of the effect of tooth brush abrasion on the characteristics of the tested restorative materials.
CAD-Temp mean wear value was 7.3322 ± 0.99853 μm. This high-wear resistance might be because the material was industrially produced in which better material homogeneity was provided hence fillers were well distributed. Furthermore, the high-molecular and cross-linked acrylate polymer with microparticle filler  in this material provided a strong bond between filler particles, more stability of the resin matrix thus less dislodgment of filler particles and equal size of filler particles. This is in agreement with Zeng et al. who observed under scanning electron microscopy (SEM) that composite resin material with size of fillers that varied greatly and weak filler bond had low wear resistance and they suggested that to improve wear resistance chemical structure of the matrix network had to be enhanced, the quantity of fillers using well-distributed fillers of a similar size should be increased and, and improve the connection between the matrix and filler.
For TempSpan, the mean wear value was 22.3165 ± 2.35459 μm. This low-wear resistance might be because the material as described by its manufacturer  have three different types of filler particles: barium, glass, silica, and alumina with different sizes, amounts, and distribution. Tanoue et al., and Teixeira et al., reported that both resin matrix and filler particle type or content were thought to affect surface conditions after toothbrushing owing to the selective abrasion of the resin matrix and the dislodgment of filler particles after long-term exposure. Furthermore, some of the properties affecting wear resistance of composite resins include size and distribution of filler particles, percentage of surface area occupied by the filler particles, filler-matrix interactions, and degree of polymerization. Furthermore in Tempspan, surface irregularities were observed under the stereomicroscope after brushing, in addition to the higher amount of wear demonstrated by the material. This could be caused by the leaching of filler particles during toothbrushing, and then acting as abrasive particles once detached from the surface.
According to the criteria and parameters of Krejci et al.,, the applied load cycles in this study were equivalent to 3 months of clinical service. Accordingly, samples were exposed to 60,000 cyclic loads with 40 N force and 1.7 Hz to resemble 3 month of clinical aging.
Evaluation of the effect of cyclic loading in this study showed three types of defects under stereomicroscope: fracture, chipping, and cracks.
CAD-Temp showed two specimens with defects following cyclic loading. In this group, only cracks and marginal chipping were observed in two specimens. In both specimens, the one with crack and the one with marginal chipping, the defects were noticed at the same place, at the proximal wall of the first premolar crown 2,683 um away from the margin. This site is the exact site of the lug attachment after milling of the interim FDP, these defects might have happened due to weakening of that wall during either cutting or finishing of the lug. Kim S and Watts DC  reported that clinically marginal breakdown of the restorations happened at a distances of 0.4-1.0 mm away from the edge, thus the distance of 2.683 mm (2683 um) is by far from the reported distance of clinical marginal breakdown.
TempSpan showed five specimens with defects following cyclic loading. The three types of defect were observed in this group. One specimen cracked at the occlusal third of the buccal surface of the first premolar crown. Two specimens fractured at the connector between the two premolars crowns. Chipping happened in two specimens 823.05 um and 58.57 um away from the margin, which is within the clinical margin breakdown reported by Kim S and Watts DC. 
Defective specimens (chipped, cracked, or fractured) following cyclic loading were excluded. Only intact specimens from CAD-Temp n = 8 and from TempSpan n = 5 were subjected to fracture test.
The fracture load values of CAD-Temp (605.1N ± 31.718 N) were almost within the range of a previous study done by Wanner  who compared the mechanical properties of three provisional blocks CAD-Temp, Telio CAD, and artBloc Temp. But the results obtained in this study were almost double that obtained by Stawarczyk et al.,  (288.9 ± 30.2N) who compared machine-made temporary (artBloc and CAD-Temp) to direct restorations and the egg shell temporaries. The lower values may have resulted from the different method used for testing.
CAD-Temp showed significantly higher fracture resistance than TempSpan, P < 0.001. There could be two reasons for this: one of them is technique dependent and the other is material dependent.
As for technique, chair-side fabrication of interim restorations is associated with some short comings affecting the mechanical strength such as mixing procedures and filling the overimpression leading to errors like incorporation of voids, compromising the mechanical strength. These human errors are eliminated in CAD/CAM technology and thus restorations produce superior results. This finding agreed with Alt et al. , who investigated the influence of fabrication technique. From the material perspective, using resin-based blanks cured under optimal conditions exhibit increased mechanical strength and prevented porosities within the restorations.  In addition to this, according to their manufacturers CAD-Temp is a PMMA material  while TempSpan is a bis-GMA material  ; many studies compared the fracture resistance of provisional materials made of PMMA to those made of bis-GMA. Almost all of them confirmed that although bis-GMA materials had higher flexural resistance than PMMA materials, bis-GMA was a brittle material and its fracture resistance was lower than that of PMMA. ,, These results were in contrast with Alt et al. , who concluded that composite based materials seem to offer clear advantages versus PMMA-based materials and should, therefore, be considered for CAD/CAM fabricated temporary restorations. Diaz-Arnold et al. results who stated that bis-GMA composites are more dense, and as a result, they demonstrated high transverse strength.
| Conclusions|| |
Within the limitations of the study, it can be stated that based on the marginal adaptation, wear resistance, and fracture resistance, the CAD-CAM based interim material is perhaps better suited to long-term interim restorations than cured resin materials.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]