TL;DR: You may be right about the negative effects of the newly emerging teeth. However, there can be also a more powerful effect of incorrect sleep associations. I recommend putting the child to sleep at the same time, alone, and leaving the child before he is asleep, so that he learns to self-soothe to sleep (Ferber, 2006).
We can spend anywhere from 30 mins to 2 hours to get him to go to
sleep, usually by rocking/cuddling to sleep.
After the predictable routine is done (bath, brushing, reading, etc), do not stay more than a few minutes in the child's bedroom. Hug and kiss your child goodnight, and leave. Do not rock or cuddle him to sleep.
Here is what Ferber (2006) recommends:
"2. Put your child into the crib or bed awake, in the place you want him to be sleeping for the night. Let him fall asleep under the same circumstances that will be present when he wakes normally during the night (in his crib or bed, not being held or rocked). Let him fall back asleep the same way after nighttime wakings." (p. 154)
"10. If your child sleeps in a crib in your room, you should put him into the crib at bedtime and then either speak to him briefly at the scheduled intervals from your bed, or—if your presence in the room is too stimulating, or if you prefer it—leave the room and come back in to check him at those intervals, as you would if he were in his own bedroom. (If he learns to fall asleep with you out of the room, you will have more freedom in the evening. You can accomplish the same thing even if you stay in the room as long as he doesn’t know you’re there—for example, if he can’t see you from his crib, or if it is fairly dark and you are quiet.) When he wakes at night, do the same.
11. If your child sleeps in his own bed in your room, use the same approach [...]
12. If your child sleeps in your bed, you may be able to lie still and withhold your responses to him for the appropriate intervals. If that isn’t possible, you may have to get out of bed and check from a chair in the room. You may even have to leave and check from outside the room [...]" (pp. 159-161)
This means that he goes
to sleep anywhere between 7.30 to 9-ish pm.
Make the routine more predictable, and bedtime repeatable to within 15-20 minutes at this age.
Regardless of what time he
falls asleep, he will always awaken magically between 11 and 11.30pm,
and will refuse food, and be very difficult to put to sleep again,
usually resulting in me and my wife getting to sleep only around 1 to
2am every night.
The child should learn to self-soothe, which typically takes between a few days and a week.
This may not be relevant to sleep, but since you give your child the evening bath, you might consider skipping the morning bath. That is, unless the child or you like this ritual, or unless a typical diaper change is not enough for some cases or "accidents". Typically, children at this age have one bath per day.
Q: Is Ferber's method the same as "crying it out", or "ignoring a child's cries until it learns not to bother with crying" (as a commenter mentions)?
A: No. It involves responding to the child at gradually increasing intervals. This method has been studied and used for decades.
Q: Is Ferber's method safe and effective? Has it been studied?
A: Yes and yes. As Oster (2019) concludes (also see references therein):
- There is evidence that using these methods improves outcomes for parents, including less depression and better general mental health.
- There is no evidence of long- or short-term harm to infants; if anything, there may be some evidence of short-term benefits.
- There is evidence of success for a wide variety of specific methods, and little to distinguish between them.
-- The most important thing is consistency: choose a method you can stick with, and stick with it. (p. 243)
Q: I heard that the Ferber method is hotly debated. Is this true?
A: I have not been able to find any scientific references about the hot debate based on research on the actual short- or long-term behavioral outcomes. Theoretically, humans have not used Ferber's method for most of the evolution. But then, humans also have not used modern sanitation, clean water, antibiotics and vaccines for most of the evolution, and these things have long ago stopped being a topic of hot debate in science.
Here is what one of the many examples of studies say about similar sleep methods: "CONCLUSIONS: Behavioral sleep techniques have no marked long-lasting effects (positive or negative). Parents and health professionals can confidently use these techniques to reduce the short- to medium-term burden of infant sleep problems and maternal depression." (Price et al, 2012)
Q: What is the minimum child age for Ferber method?
A: I could not find a research-based answer quickly. From personal experience, it is about 4-6 months, when the children stopped requiring the feeding in the middle of the night (e.g., when they were capable to sleep through the night without requiring an adult based on feeding).
Q: How important is teaching the child to self-soothe? Is this something he can eventually learn as he grows older?
A: Most children learn to self-soothe as they grow older. From personal experience, I have not seen that it is very important for the child to learn this skill as early as 6 months, and specifically using Ferber's method. We decided to use it because it is safe and effective, not because it was critically important to the child.
Ferber, Richard. (2006) "Solve Your Child's Sleep Problems: New, Revised, and Expanded Edition" New York, NY: Fireside: https://www.amazon.com/dp/0743201639/
Emily Oster. (2019) "Cribsheet: A Data-Driven Guide to Better, More Relaxed Parenting, From Birth to Preschool." New York, NY: Penguin Press: https://www.amazon.com/Cribsheet-Data-Driven-Relaxed-Parenting-Preschool/dp/0525559256
Anna M.H. Price, Melissa Wake, Obioha C. Ukoumunne, Harriet Hiscock. Five-Year Follow-up of Harms and Benefits of Behavioral Infant Sleep Intervention: Randomized Trial. Pediatrics Oct 2012, 130 (4) 643-651; DOI: 10.1542/peds.2011-3467 : https://pediatrics.aappublications.org/content/130/4/643.long