Introduction

Poor marginal adaptation in dental restorations causes cement dissolution. This can lead to plaque accumulation, recurrent caries. Dental pulp inflammation, periodontal disease and finally treatment failure. (1, 2, 3, 4, 5, 8, 13)

Metal ceramic restorations are still the gold standard choice of fixed dental prosthesis. Popularity of metal ceramic restorations is due to their strength and marginal adaptation. Unfortunately, these restorations are like a barrier prevent light transmission through restorations (18, 29)

If esthetic is essential, we should use collarless metal ceramic or all ceramic restorations, Marginal adaptation of these restoration is lower than cast metal ceramic restorations but clinically acceptable.(7)

High strength cores of alumina and zirconia made them as an excellent material in anterior and posterior metal free restorations in all types of occlusions. Marginal adaptation is a normal concern in this restorations (4) CAD/CAM method improved design, fabrication and accuracy of dental restorations. It is faster, accurate and comfortable. Although today chair side in office method of fabrication needs more time and cost, probable errors such as scanning procedure, software designing, milling and distortion during and after sintering can affect marginal adaptation (14-17)

    Novel sintron technology introduced by Amman Girrbach company, allowed chrome-cobalt soft milling without cooling agent and difficulties. Advantages
are: 1) simpler and comfortable milling

2) No need to wax up, investing, casting steps 3) maximum speed, time saving

4) Accuracy because of digital technology    

5) Avoid repeated sending to dental laboratory 6) in office fabrication. (22)

The purpose of this study was evaluation and comparison of marginal adaptation in metal ceramic and all ceramic restorations fabricated by two methods: CAD/CAM and conventional.

Materials and methods

      1. Cast and die production

In this in-vitro study, first, one upper jaw and one lower jaw plastic model of dental arches selected and hand articulated for better stability after die preparation. The upper first molar selected and prepared for complete coverage crown with an 1 mm depth round shoulder finishing line manually. Then each die surveyed to avoid undercuts. Afterward, impression done by additional silicone material and after pouring with gypsum, working cast and die were fabricated. (Fig. 1)

2. Restoration fabrication

60 restorations divided into 6 groups (n=10) Groups A, B, C were metal ceramic and groups D, E, F were all ceramic. (Fig. 2)

* Group A: Conventional wax up method used to producing wax copings and then converted to metal copings by lost wax technique. Porcelain layering done and then shoulder porcelain

Added with direct lift technique. (Fig. 3)

Group B: in this group wax copings made from CAD/CAM able wax blocks and converted to metal copings by lost wax technique and then porcelain layering and adding shoulder porcelain done like group A. (Fig. 4)

Group C: in this group sintron technology used. Copings were milled from soft presinterd chrom cobalt alloy by CAD/CAM and then sintered in special oven under pressure of agron gas. Final strength of these copings is comparable with conventional method. Adding porcelain steps are like group A (Figure. 5)

Group D: Restorations of this groups were lithium disilicate (e max-press). First a full contoured wax up performed. After lost wax technique e max ingots pressed to the mold space by special plunger. Finally a full contoured all ceramic restoration produced. (Fig 6)

Group E: Restorations in this group were named zircon. Zircon core milled by CAD/CAM from
pre-sintered zirconia blocks. Then sintered and porcelain layering done. (Fig. 7, 8)

Group F: restorations in this group named Zolid. Full contoured restoration milled from pre-sintered zirconia blocks by CAD/CAM and then sintered in special oven. (Fig. 9)

3. Marginal gap measurement

For this purpose, replica technique used. Silicon replica of all restorations sectioned as seen in fig 10.
8 points of each silicon replica measured by optical stereomicroscope under 60X magnification. (Fig. 11)

Statistical analysis

In this in vitro study, at first Shapiro-Wilk test was done for evaluating data normality. It was found that data in some groups have not normal distribution. Kruskal-wallis test used for data analysis and comparison in each 6 groups. Mann-Whitney test used for data comparison between metal ceramic and all ceramic groups.

Figure1.Upper and lower dental arches

Figure 2.60 fabricated restorations

Fifure 3.Conventional casting metal coping

Figure4.CAD/CAMable wax blocks

Figure 5. Presintered soft chrome cobalt blocks

Figure 6.e.max Press ingots and plunger

Figure7. CAD/CAM designing

Figure 8. Presintered zircona blocks

Figure 9. Presintered Zolid blocks

Figure 10.Occlusal view of replica and 8 measurement points

Figure 11. Photographs of cross sections of replica

        Results

In this study, marginal gap of two groups of the restorations (metal ceramic and all ceramic) and their subdivisions (A, B, C, D, E, F) measured. As it can be seen in table 1 the lowest mean marginal gap was in group C and the greatest in group E. There was significant difference between 6 groups statistically (p<0,001). In paired comparison between 6 groups, it was found that mean marginal gap in group C was significantly lower than groups A, D, E, F. Also mean marginal gap in group F was lower than groups D and E. Groups F and D also were significantly lower than group E. Between other groups there was no significant difference. (Table 2) Data distribution in 6 groups has shown (Chart 1). As you can see in this chart, there are large gaps in groups 3 and 5.

Regarding the table 3, the lower mean marginal gap existed in metal ceramic restorations and the difference was significant statistically (p<0,001).Data distribution between metal ceramic and all ceramic has shown in chart 2.

 Table1 .Mean، Standard of deviation, minimum, maximum and median marginal gap measurement
of the study groups

Table 2.Paired comparison of 6 groups of the study

Table3. Mean، Standard of deviation، Minimum، maximum .Median Data of marginal gap of metal ceramic and all ceramic restorations and their statistical results

.

Chart 1. Marginal adaptation data distribution status for all study groups separately

Chart 2. Marginal adaptation data distribution status for metal ceramic and all ceramic groups