Flow injection or bonding: when composite is better injected and when sculpted

The question usually comes in the same form: if in both methods the tooth is rebuilt with composite and in neither is healthy enamel ground down, why two names? The difference is not in the material but in the moment the decision about shape is made: at the chair or before it. That determines how many visits the work takes, how repeatable the result is and where corrections are made when something is not right.

The same composite, a different moment of decision

In bonding the dentist applies composite in layers directly to the tooth and shapes it by hand, with the working field isolated and under magnification. The shape is created during the treatment and corrected during the treatment: the biting edge, the curvature, the transition to the neighbouring tooth. The result is assessed live, on this tooth, in this light.

Flow injection reverses this order. First comes an intraoral scan or an impression, then a design of the shape of the teeth outside the mouth, then your approval, and the material comes into play only at the very end. We inject flowable composite into a clear silicone key taken from the approved design and cure it in that shape. What remains in the practice is reproducing what was agreed earlier.

The practical consequence is one: in bonding you make corrections on the tooth, in flow injection on the design.

When bonding is simpler

Bonding wins wherever the task is localised and the new part has to blend into what is already there. When the restoration concerns one tooth, a silicone key adds little: what is needed is a layer matched in colour and translucency to the neighbour rather than a repeatable outline.

• One or two teeth: a chipped biting edge, a defect after an injury, a single lateral incisor that differs in shape
• A correction that has to fit between the neighbouring teeth, not change them along the way
• A tooth with its own character, with discolouration, a streak or a visible transition line, where the layer counts, not the outline
• A situation in which you want a single treatment visit: the treatment itself takes 60–90 minutes
• Adding to an earlier restoration, when the rest of the smile stays unchanged

In work like this, many decisions are only made at the chair, because only then can you see how the new layer behaves next to the old enamel. Bonding leaves the dentist that freedom and closes the matter the same day.

When flow injection is better

The more teeth in the plan, the harder it is to keep the same length, the same edge angle and the same width on both sides of the midline by hand. The key transfers the approved design to each tooth in turn, so symmetry does not depend on which tooth in the row it is or what hour of the treatment.

• The whole front section: most often six to eight teeth, although sometimes two are enough
• A diastema and gaps between teeth that need closing in one consistent plan
• Worn biting edges after years of clenching or erosion: length has to be restored on several teeth at once
• Small or peg-shaped teeth, where the proportion changes rather than a single detail
• Finishing orthodontic treatment: the teeth are already where they should be, and only the shape is left to improve
• The need to see and approve the shape before anything stays on the teeth permanently

The design itself can be made in two ways: from a diagnostic model or digitally, after an intraoral scan. From the approved version we take the key, and because it is clear, we cure the composite with light through it, without removing the mould. That is why the shape from the try-in and the shape that stays on the teeth are the same shape, not a reproduction of it from memory.

The process: one visit versus two

Both paths start with a consultation: 30–45 minutes, intraoral photos, a written treatment plan. Then they diverge, because the design stage falls in a different place in each.

1. Bonding: a visualisation of the shape on an intraoral scan or photograph, to approve before the treatment.
2. Bonding: a 60–90 minute treatment, with the working field isolated and under magnification, finished with polishing.
3. Flow injection, first visit: an intraoral scan or impression, photos and a design of the shape of the teeth to approve.
4. Flow injection: a try-in of the design in the mouth, with no drilling; you see the shape before it becomes permanent.
5. Flow injection, second visit: injecting the composite into the key, curing, finishing the edges, polishing and checking the bite.
6. After both methods: a follow-up visit after the treatment and contact with your dentist for 14 days.

The extra visit in flow injection has a specific purpose. It holds the try-in, the moment when you can reject the shape before anything is fixed on the teeth.

What neither method takes care of

Composite completes treatment on the aesthetic side, but it does not replace it. Before the restoration, decay must be treated and the gums must be healthy, because composite bonds to etched enamel and needs a dry working field, which a bleeding gum makes impossible.

• Crowding and rotations: composite masks small deviations; with larger ones the teeth are aligned first and the shape improved afterwards
• Colour: we match the shade of the composite to your own teeth, so if you are planning whitening we do it before the restoration, and choose the material only once the colour has settled
• Hygiene visit: colour is chosen on clean enamel, and deposits hinder the composite’s adhesion, which is why a hygiene visit comes before both methods
• Bruxism: with clenching and grinding, composite wears faster, and we agree how to protect the restoration together with the plan

What the durability of the result depends on

Composite is a material that wears regardless of the application technique. Over time it loses its shine, absorbs stains from coffee, strong tea and red wine, and with night-time clenching it wears down at the biting edges. With bonding we usually speak of the full effect lasting 5–8 years, with regular hygiene and check-ups every six months.

More important than the number itself is that composite can be repaired locally. A stained edge, a worn margin, a small chip: most often it is enough to add material and polish, without touching the rest of the restoration. This applies to both methods and is one of the reasons why it is worth starting with a reversible solution.

What this decision looks like in the practice

The method is not chosen by name but after an examination. At the consultation in Oliwa, Gdańsk, we check the position of the teeth, the condition of the enamel, the bite and the real scope of work, that is, how many teeth need to be in the plan at all if the result is to look consistent rather than just different in one place.

Sometimes the answer is a combination of both techniques: the front section recreated with a key, and one tooth that, after the key is removed, still differs in character from its neighbours, refined by hand at the same visit. You receive the treatment plan in writing, together with the scope and number of visits, before we start anything.

Start with a consultation

At the consultation we check the scope of work, the bite and the condition of the enamel, and choose the method to match what we see. You receive the treatment plan in writing.

See flow injection