In porcelain dental restoration, no fitting margin and high occlusion account for a large proportion of reasons for failure of repair and remake. Doctors and technicians have different opinions about these two problems generally，and it is also the focus for them to evade responsibility.

A .Margin not fit and high occlusion happens at the same time，and the technicians and doctors think it is the crowns not in position，So what’s reason for not in position?

First，in clinical aspects：

1．Doctor Preparation: Abutment not smooth or has fulcrums，irregular

shoulder preparation，slight difference in path of insertion. So smooth abutment ，regular shoulder design and the same path of insertion in preparation should be guaranteed for doctors.

2．The coefficient of expansion is not good as water not mixed correctly according to the instructions with the gypsum，so the margin of stone models has gaps to the real one. 3．Applying two different kind of gypsum in pouring models. The first layer is superhardone，the second just hard gypsum or common ones，so different contraction proportion caused the slight changes of common path of insertion. This will be solved to when same kind gypsum used.

4．Common gypsum to pour models sometimes cause errors, super hard one is better.

5．Not immediately pouring out models after trays got，so the slight shrink of dental impression material caused deviations.

 

 

In the second，for the technicians：

1. Die cutting for restoration is not accurate，there is gaps between die and the base，results in high occlusion and margin not fit.

Solutions：Keep the clean of the die boxes，to check if there is gypsum slag in it or stays in the contacting area of boxes and die. If pins are used，fixation holes should be kept clean，to avoid gypsum slag left in it.

2.Die rocking，slight change for common path of insertion.
Solutions：To check if the pins are pasted tight and absolute parallel；if water proportion and solidity of gypsum of the base is suitable；If pin caps used，we should check if they are closed and with appropriate tightness.
 
3.Cutting the contact points of adjacent teeth in die cutting and shape trimming，so the crown can not be fully in position as there isfulcrums.
B. Only margins not fit which mainly caused by models has below reasons：
Reasons for doctors：
 
1. No gum distinguish line marked and not taking impressions by silicone materials . If gum distinguish line can not reachperiodontal，gum distinguish grease can be used；We can also use aga and alginate material for impressions taken. But doctors should noted that gum distinguish line and accurate impression materials should be used together，or it is difficult to get afit margin for the ceramic crowns.



 
1. The coefficient of expansion is not good as water is not mixed correctly according to the instructions with the gypsum，so the margin of stone models has gaps to the real margin.
 
2. Not using superhard gypsum for pouring models，common gypsum always has deviations.
 
3. Margin has bubbles when pouring models.