Normally, I'm a big fan of dumbbells, however this might be a point where you might consider switching to barbell.
The reason I suggest is if you have access to 40lb and 45lb dumbbells, I'm assume you are at a gym. As such, I assume you probably have access to a barbell.
While dumbbells are great for addressing imbalances, especially in upper body lifts, there is less carry over for lower body lifts. Depending on your circumstances there are two possible options for you.
When holding the dumbells, your arms are going to be doing the majority of the stabilsation work, however they will be fixed to your hips. Similarly, the major muscles in the squat are working to push the hips up, and less stabilisation will be required by these muscles.
So unless you have a particular reason against switching to a barbell, which will likely be easier and safer to handle at this weight, that might be and alternative option.
Try a different exercise
If you can't access a barbell, look at what other exercises might fit your needs. People often overlook single-leg squats or similar alternatives that allow you to still work your legs with leg weight.
An excellent option is the Bulgarian Split Squat, while not a completely uni-lateral exercise, it gets many of the benefits of them single.
In essence, you stand in front of a bench, with one foot resting on the bench, while you squat with the other upright leg. Perform for the desired lot of sets and switch legs. The benefits of this exercise over dumbbell front quats include:
- Since you hang your arms to your sides, you don't need to raise them into position
- Improved progression potential, as you move less weight. Since its a near single-leg movement, don't be surprised if you drop to 50-60% of the weight you were move previously.
- Excellent stabilisers training
- Short exercise times, since one leg is "resting" while the other is working, you reuqire less gaps between sets.