6 Steps to a Perio Diagnosis

I’ll confess something. When the 2017 classification arrived, a lot of colleagues looked at it the way most people look at flat-pack furniture instructions: lots of diagrams, a vague sense of dread, and a quiet plan to just wing it. “Aggressive” and “chronic” were gone. In came staging, grading, extent and current status. It felt like learning a new language halfway through your career.

Here’s the good news. Once you know the order, perio diagnosis is one of the quickest things you’ll do all day. With radiographs and a BPE or pocket chart in front of you, it takes under two minutes. I always work through it as six steps, because that’s how I actually do it in clinic, and because a diagnosis you can do quickly is a diagnosis you’ll actually do.

And it matters. Formulating a diagnosis has to happen before any treatment plan. Patients also need to know their periodontal diagnosis, both medico-legally and because you can’t commit to managing a condition nobody has named. A diagnosis is the postcode you type into the sat nav. Without it, you can drive very confidently in completely the wrong direction!

Step 1: Is This a Periodontitis Patient?

This is the step people underestimate. Once a patient is diagnosed with periodontitis, they are a periodontitis patient for life. Successfully treated, beautifully maintained, bleeding barely at all: still a periodontitis patient. It’s a bit like being a former smoker. The habit may be gone, but the history still shapes the risk, and the patient needs to know it so they keep up supportive periodontal care.

One caveat: bone loss isn’t always periodontal. Surgical extractions, crown lengthening and other pathology can all remove bone. Make sure you’re blaming the right culprit.

Step 2: Extent

How widespread is it? Look across the radiographs and count:

• Localised: up to 30% of teeth affected
• Generalised: more than 30% of teeth affected
• Molar–incisor pattern: first molars, with or without incisors

Don’t skip the molar–incisor pattern. It is the diagnosis most likely to be sitting undiagnosed in a young patient whose gums look fine and whose first molars tell a very different story.

Step 3: Stage

Stage is severity, meaning how much damage has already been done. Pick the tooth with the most interproximal bone loss and look at how far down the root it goes:

• Stage I: less than 15% bone loss (or under 2mm from the CEJ on bitewings)

•  Stage II: coronal third of the root

• Stage III: middle third

• Stage IV: apical third

If a patient has clearly lost teeth to advanced periodontitis, you can classify them as Stage IV on a case-by-case basis.

Think of stage as a look in the rear-view mirror. It tells you how far the disease has already travelled. It doesn’t tell you how fast it’s going.

Step 4: Grade 

That’s what grade is for. Grade reflects the patient’s susceptibility, and it predicts future disease in the absence of treatment. If stage is the rear-view mirror, grade is the speedometer.

The quickest method needs only two numbers: the worst bone loss as a percentage, and the patient’s age.

• Grade A: percentage bone loss is less than half their age

• Grade C: percentage bone loss is more than their age

• Grade B: everything in between

So 50% bone loss in a 70-year-old is Grade B. The same 50% in a 35-year-old is Grade C, a very different conversation. Same radiograph, different biology. Grade is where age stops being a detail on the patient’s notes and becomes clinically meaningful.

Step 5: Current Disease Status

So far, everything has been about bone. But a radiograph is like a photograph, not a live feed. It shows you that bone has been lost, but not when. That loss could have happened years ago and been quiet ever since, or it could still be happening now. That’s why Step 5 matters. The radiograph tells you the history. The probe tells you what you’re treating today. The patient is one of:

• Stable: healthy or successfully treated

• In remission: bleeding on probing at 10% of sites or more, but probing depths of 4mm or less, with no 4mm site that bleeds

• Unstable: bleeding at sites of 4mm or more, or any probing depth of 5mm or above

Think of this as your traffic light. Stage and grade tend to be the fixed characteristics of the patient. Status is the part that changes, and it’s what your treatment is trying to move from red to green.

Step 6: Risk Factors

Finally, record whether the patient smokes (or used to) and whether they have diabetes. These go into the diagnostic statement itself because they can be measured and controlled. Other relevant factors, such as stress, family history and medications, go on a separate line. They still matter, because they complete the patient’s “causal pie”.

Putting It Together 

A 45-year-old patient. The worst tooth has bone loss into the middle third of the root, about 50%. More than 30% of teeth are affected. Several bleeding 5–6mm pockets. Smokes 15 a day.

1. Bone loss from periodontitis → periodontitis patient

2. More than 30% of teeth → generalised

3. Middle third → Stage III

4. 50% bone loss at age 45 → more than their age → Grade C

5. Bleeding pockets of 5mm+ → currently unstable

6. Risk factor: smoker

When you write it out just swap round 1 and 2: Generalised periodontitis, Stage III, Grade C, currently unstable. Risk factor: smoker.

That took less time than it took the patient to find their glasses! And look at how much it tells you: severe disease, high susceptibility, active right now, and a modifiable risk factor sitting in plain sight.

Why the Statement Matters More Than You Think

A diagnostic statement isn’t just admin. It’s the whole treatment plan in shorthand. Stage tells you how complex treatment is likely to be. Grade tells you how hard to push and how closely to monitor. Status tells you whether you’re treating or maintaining. The risk factors tell you what the patient has to change. It also gives every clinician who opens the notes the same starting point, which is far better than six people each forming their own vague impression.

It’s also the basis of the conversation with the patient. Use the proper word: periodontitis, not “a bit of gum trouble”. Explain the stage as mild, moderate, severe or very severe. And use grade as the hook. For a Grade C patient, it’s honest to say they are highly susceptible and that, without treatment, the risk of tooth loss is high. That sentence changes behaviour in a way “your gums need some attention” never will.

The Two-Minute Rule 

None of this works without the inputs. You need good-quality radiographs where the bone levels are visible and a proper pocket chart. Step 1 can’t happen from a glance at the gingiva, and Step 5 can’t happen without a probe. If you’re missing either, the diagnosis isn’t slow. It’s impossible.

With them in front of you, there’s no reason any periodontitis patient should leave without a diagnostic statement in their notes and an explanation they understand. Six steps. Two minutes. Every time.