The line counting technique is a powerful technique that many pre-dental students have been using to do well on the top/front/end section of the Dental Admissions Test (DAT). On this page I will explain to you how the line counting technique works, and how to use it effectively on the Perceptual Ability section of the Dental Admissions Test (DAT).
Listed below are the top 3 most popular perceptual ability resources for explanations and practice problems.
The Top/Front/End section of the Dental Admissions Test consists of questions in which you are given two projections of an 3-Dimensional object, you must then determine the third projection, in these problems you see two types of lines, invisible lines (represented as dashed lines), and solid lines, which are substructures you can see from your projection. Below is a practice problem and an explanation of the Top/Front/End View.
The diagram below helps you visualize what the question is asking for when it asks for a certain projection. Imagine the arrow is your eye looking at the projection from a certain angle. For the top projection imagine you put the 3-D object on a table and you stand up directly above it and look down at the object. For the front projection imagine you put the object on the edge table and kneel and looked at the object in such a way your eyes were level with the center of the object. Now for the end project imagine you still are viewing the object in the direction as the front projection but now you turn the object 90 degrees to the left, you will now see the end view of the object.
Imagine your eyes are at the beginning of the arrow, in this diagram.
Now lets talk about invisible lines next in this tutorial. Invisible lines may seem very confusing, but they are a great tool to use to help you identify the third projection in a top/front/end view problem. Invisible lines are substructures hidden within an object that are not seen from your projection but are there and are indicated by dashed lines. The diagram below better explains this:
If you were to look at this figure from the top view you would not be able to see this substructure below it (Highlighted in Red).
This structure would be represented by the dashed line colored in red on this question.
The basic premise of the line counting technique is to count the number of lines in a given projection and compare it to the answers given, making sure you keep track of invisible lines. So lets try this practice problem and I will walk you through the steps.
So lets use the line counting technique using only the end view first. Now count the lines from the bottom up just like in the figure below making note of the invisible lines.
From the End View we have determined that there are four lines and that:
Line 4 is a solid visible line.
Line 3 is a dashed invisible line.
Line 2 is a dashed invisible line.
Line 1 is a solid visible line.
Now because all these lines stretch from one end to the other on the entire figure, we can conclude that they should all be visible from the front view. Using that conclusion, lets use the line counting technique to eliminate some of the choices.
Choice A Cropped and blown up for ease of visualization
Choice A Does not work for 2 reasons
Using the line counting technique, and looking at this figure we have determined that:
Therefore we can conclude this may be a possible answer, but lets check the other selections just to make sure.
Using the line counting method we have determined:
Using the Line Counting Method we have determined:
Now lets see what we have to choose from…
Using the line counting technique we have eliminated 2 choices, just by counting lines. The fun part is that we can use the line counting technique on the top projection, to help us find the right answer!
Line 5 is a solid visible line
Line 4 is a solid visible line
Line 3 is a dashed invisible line
Line 2 is a solid visible line
Line 1 is a solid visible line
Choice B does not work for a number of reasons:
Now lets check out a cropped and enlarged choice D to see why it is the answer
I hope this review helped you all out, post comments below if you have any questions!
Listed below are the top 4most popular perceptual ability resources for explanations and practice problems.