Read the mouthing and wriggling correctly
A young puppy grabbing the brush is rarely being difficult. The brush approaches his body, moves oddly, and smells interesting, so mouthing it is exploration, and the wriggling is usually a simple statement that he has had enough stimulation for now. Puppies also have short tolerance for stillness, and grooming asks for stillness plus strange sensations plus restraint all at once. The fix is to shrink the job until it fits inside the tolerance he actually has, then grow both together.
Timing does half the work. A puppy after a walk and a play session, heading toward a nap, can accept handling that a freshly woken, fully charged puppy cannot. Building grooming into the sleepy end of his rhythm, rather than battling him at his most energetic, changes the whole character of the exercise.
Thirty-second sessions with his mouth otherwise employed
Give his mouth a legal job: a lick mat stuck to the floor or a low surface with a smear of something tasty, or a chew held by a helper, frees his teeth from brush duty. Start with one easy area, usually the back, where strokes feel least intrusive, and do a handful of slow strokes, feeding or letting him lick between them. Stop at around thirty seconds, or sooner if he starts turning toward the brush, and finish with play or a treat so the session ends as a good event.
Across days, add one area at a time in a difficulty order that suits him, often back, then sides, then chest, with legs, tail, ears, and tummy last because they are the most sensitive and ticklish. Let him sniff and mouth the brush freely on the floor outside sessions, because a tool he can investigate at his own pace loses its novelty value as a thing to grab mid-stroke. Use a soft brush matched to a puppy coat at this stage, since a harsh tool on tender skin gives him a genuine reason to object that no amount of treats will argue with.
Build duration and handling, not battles
Increase session length by small increments, a minute, then two, as he stays relaxed, and weave in the handling grooming will eventually require: lifting an ear, holding a paw, parting the coat to skin, each rep paid with food. If he escalates mid-session, wriggling harder, grabbing, or starting to pant and fuss, the session was too long or the area too difficult; end kindly and make the next one easier rather than holding him through the protest to finish. A puppy pinned until he gives up learns that grooming is something done to him against his will, and that lesson resurfaces, larger and stronger, in the adult dog.
Some wriggling is simple adolescence arriving early, and on those days a shorter session with more lick-mat time is the right answer rather than abandoning the day's grooming entirely, because frequency maintains the habit even when duration cannot.
Toward a grown-up grooming routine
As his adult coat comes in, his grooming needs will grow, more thorough brushing, possibly professional grooming visits, and the early groundwork pays off there too: a dog who knows brushes, handling, and table-like surfaces from puppyhood arrives at a groomer as a routine client rather than a problem. A trial visit to a groomer for a tiny puppy session, a bath or just handling and treats, extends that familiarity before a full groom is ever needed.
Keep the home sessions on a regular rhythm, little and often, and note which areas he accepts, which still need work, and what settles him best. Assigning those short grooming slots between family members on KinsLe with Care Teams, each one ticked off with its timestamp, keeps every session brief and consistent instead of one person attempting an exhausting full groom that sets the habit back.