If you’ve always been terrified of dental work and the idea of someone poking around your pearly whites with sharp tools, you’re not alone. With “Insidious: Out of the Further,” the sixth entry in the infinitely inventive horror franchise, writer-director Jacob Chase is unashamed to declare that he shares your fears, while having some gross-out fun with this widespread irrational phobia.

A largely setpiece-driven chapter with a wobbly story but several impeccable vignettes that drill into our deepest bedtime anxieties, “Out of the Further” (like the rest of the films in the series) follows a group of unlucky humans plagued by demonic spirits that live in a dream space called “The Further,” and occasionally travel into the real world to hijack pockets of life and energy. And some of the film’s most impressive frights take place in the dentist’s chair, veering into serious body-horror territory.

It’s not that Gemma (Amelia Eve), the young single mother and dental hygienist that leads the film, has any sadistic intentions à la “Marathon Man” or “The Dentist,” even though Chase surely had those films in mind to some degree, while slightly flipping the script on them — making the patient, not the provider, the main perpetrator. In one of the most effective scenes, an old man (David Morgan) with rotting teeth, and quite possibly a second set of much sharper fangs, terrorizes and injures Gemma while she scrapes off sizable heaps of slimy residue from his mouth, even pulling out strands of hair as he silently stares at her. (Feel free to either gag along or close your eyes.)

The patient in question is one of a trio of dead people strolling around Gemma’s neighborhood; another is styled in such a hagsploitation manner that it’s impossible not to think of Aunt Gladys from “Weapons.” The entities continually lurk into Gemma’s house and into the eyes of her precocious nine-year-old daughter, Maya (Island Austin), trying to intimidate the family of two. It’s actually curious that Gemma chose to stay in that same house after the events of the terrific opening prologue, set in 1999, in which the young Gemma (Charli Penton, brilliant in a short role) witnesses the brutal death of her fragile mother through an inexplicable series of supernatural happenings.

Twenty years later, she wants to be a different kind of mother to her school-obsessed daughter, encouraging her quirks (like her insistence on building little crawl spaces out of couch cushions) and being emotionally present. But her kindly and supportive cop boyfriend Nick (Brandon Perea) rightly insists that the duo should perhaps move out of the house when Gemma’s habitual nightmares intensify. As she goes deeper into the Further in her dreams, she occasionally and unwittingly brings back a spirit or two. But little does Nick know that it is Gemma, and not the house, that is haunted.

Chase’s script doesn’t spend a lot of time explaining the idea of “The Further” to those unfamiliar with the franchise, the concept is still basic enough to follow: It’s a world that supernaturally gifted people like Gemma travel to while sleeping, crawling with demons, all looking for a living being to latch onto. While Gemma is in the Further, the film unleashes a number of polished horror sequences, the most frightening one turning Maya’s crawlspace into an airless, claustrophobic maze that wouldn’t be out of place in “Backrooms.” With effective sound design and customary jump scares, “Out of the Further” knows exactly what it wants to be for a while: an atmospheric, vibes-based horror film that will make any nervous sleeper check under their bed before turning the lights off. You know, just in case.

But the story’s shortcomings rise to the surface in due course, especially when Elise (Lin Shaye) — the franchise’s most beloved character, now deceased — re-enters the picture as a ghost who helps people like Gemma find their way back home. In this chapter, Elise communicates to the living via Clare (Maisie Richardson-Sellers), a talented tattoo artist and a selfless medium invested in helping Gemma and Maya get rid of Lester (Joseph Lopez), the main demon who wants to make our world a playground for his kind.

A scene where Clare tries to explain Elise’s plan to Gemma, Nick, and Maya using a bunch of cut-up oranges makes so little sense that one wonders if the writers were trying to convince themselves first and foremost that the convoluted scheme is actually quite simple. (It’s far from it.) If the first two (and best) “Insidious” movies have taught us anything, it is that the fear of losing one’s family, and knowing that the only way is out is through, is enough of an emotional terror. While Chase’s film captures that feeling soundly for a while, with both Eve and Austin painting a beautiful mother-daughter portrait, it also makes you wish for a leaner resolution in its later moments.

Still, there is much old-school horror fun to be had here, with costume designer Liz Keogh Palmer and the team of makeup artists especially deserving of credit with their mind-blowing work on various evil spirits. Many of them might just make an appearance in your consciousness when the lights go off.