Lower Denture Implants: One 2-Locator Overdenture Retrofit, End to End

1. The Case at a Glance

Two things in that table drive every decision below.

The patient's existing lower denture was the input. We did not design the tooth setup, the arch form, or the border. The patient and the clinician had already lived with those shapes for years.

The upper arch is a conventional denture, and that has teeth. On a maxillary denture that depends on peripheral seal, a rigid bar on the lower can unseat the upper. A literature review on mandibular overdentures sets out the mechanism: where a maxillary full denture opposes the overdenture, stud attachments rather than bar attachments are preferred, to avoid forces that could destabilise the maxillary denture (literature review on mandibular overdentures, PMC10874113). So "2 Locators, not a bar" here was not a preference of ours. It was a mechanical requirement coming from the opposing side.

Two implants in the canine region for a lower overdenture is a well-established pattern, not an improvisation. An overview of mandibular implant overdentures states it directly: for an edentulous mandible, a two-implant overdenture is generally accepted as the standard of care rather than a conventional denture, and long-term studies confirm satisfactory results with only two implants (prosthetic overview of mandibular overdentures, PMC6196685).

2. Patient Situation — What Was Actually Wrong

The clinician's note to us was short, which is normal. The three lines that mattered:

1. "Lower will not sit still — rocks on function, lifts on talking."
2. "Patient does not want a brand-new denture. Attached to this one."
3. "Already placed two implants, 3 months post-placement, uncovered and ready to load."

In plain language: the patient had made peace with the shape, the colour and the bite of the lower denture. What they could not make peace with was a lower that goes for a walk every time they eat. That is a specific, repeated complaint in this patient group. A conventional lower denture rests on the gums instead of anchoring into bone, and that is precisely why it shifts, slips and rocks in a way an implant-anchored restoration does not (Cleveland Clinic reference on implant-supported dentures). It also explains why the durable fix is mechanical rather than another round of border adjustment.

Two things the clinician did not ask for, which is also information:

• No change in vertical dimension. The occlusion against the upper was workable; we were told to preserve it.
• No change in tooth position or shade. The patient recognised the smile. We don't touch what the clinician told us not to touch.

A lower denture implants retrofit is, by nature, a job defined as much by what you don't move as by what you do.

3. The Clinician's Prescription — What They Asked, Line by Line

Here is the request as it reached us, trimmed to the parts that drove lab decisions:

• Two Locator abutments, lowest-profile inserts to start. The clinician wanted to begin at the softest retention and let the patient tell them when to step up.
• Pick up the housings in the existing denture, no remake. This is the retrofit route — mill a housing seat into the current acrylic, pick up or lab-process the metal housing, done.
• Preserve the occlusion against the existing maxillary denture. No vertical change, no major tooth-position change.
• Reinforce the base where the acrylic will be thinned. This denture had been in service for years; the mid-line resin is not as thick as a brand-new base.
• One try-in before final. A single verification visit, so the clinician can confirm fit, retention and occlusion before the housings are permanently processed.

Translated into bench work, the brief was five tasks: measure, mill, reinforce, process, balance. Everything downstream is one of those five.

4. How We Met Each of These Requirements

This is the long section, because it is the only one that is actually ours. Clinical decisions belong to the clinician. What follows is lab work.

4.1 Case Intake and Digital Setup

The case came in through our standard case-coordination route. The scans and the physical denture arrived together — the patient's current lower denture, impressions with Locator impression copings in place, and a bite record against the upper. Our case coordination team logged it, the CAD team opened the files, and the Implant Department (around 80 technicians in-house, part of the ~460-person Shenzhen floor) took it on.

Here is the exact split we used:

All of it sits inside our own facilities. We don't send Locator work out — the chain from CAD to QC runs on our bench. For a retrofit specifically, that matters: the acrylic coming in is not a blank, it has history, and anything that changes hands adds a chance to misread what the clinician asked us to leave alone.

4.2 Why Locator and Not a Bar

The choice is the clinician's, but the lab needs to know the ground rules.

Two options sit on the table for a 2-implant lower overdenture: a stud attachment (Locator being the common one), or a connecting bar with a clip. Both work. A prosthetic overview of mandibular overdentures sets out the mechanical difference: implants splinted together with a bar resist micromotion and axial rotation, and splinting produces a more favourable stress distribution at the implant-bone interface (the same overview). A stud attachment is the non-splinted route, with each implant carrying its own load. Once the opposing arch enters the picture, the two systems stop being interchangeable. For this patient — opposing a conventional maxillary denture, and a retrofit of the existing lower — stud attachments were already the right call before any of us got involved. Antagonist effects on the maxillary denture pushed the decision toward Locator (the same review).

So the lab-side question narrowed to one thing: can the existing lower denture accept two housings without losing the strength it needs?

4.3 Measuring Before Milling

Before we hollow out acrylic, we measure what is there. On this denture:

• We registered the base against the master cast with housing analogs in place.
• We scanned the tissue side and the polished side together, so the CAD view shows acrylic thickness at every point.
• We marked the two housing seats and read off the remaining wall thickness around and under each seat.

If that remaining wall is thin — and on an older denture it often is — the plan has to carry a reinforcement step. We don't guess. The scan tells us.

4.4 Milling the Housing Seats

Our Milling Department (about 70 technicians) handled the subtractive step. Two notes about this on a retrofit:

• The seat is not just a hole big enough for the housing. It is a shaped pocket that leaves a tissue-side rim, so the housing seats passively on the abutment rather than loading the denture base. That rim is what keeps the housing from levering the acrylic in function.
• The path of insertion is defined by the abutment pair, not by the denture. If the implants are not perfectly parallel — and they almost never are — the pocket shape has to absorb that divergence within the Locator system's tolerance.

For this patient, the two abutment heights were not equal, so the pocket depths were set independently, and those depths went into the case file so the clinician can see what was done and why.

4.5 Reinforcing the Base

Where the acrylic is milled thinner, the base needs help. On this case we laid a metal-mesh reinforcement into the resin on the inner surface between the two housing sites, processed in during the housing pickup. We don't publish a "we always use X mesh at Y mm" recipe, because the right call depends on the base thickness we actually measured. On this one, mesh plus thickened polymer around the housings was enough. The sequence is check first, then decide.

Worth flagging the failure mode here, because this is where a retrofit goes wrong months later. Attachment-related problems are the maintenance pattern on this type of restoration. With ball abutments the principal prosthetic complication is fracture of the denture base; with Locator abutments it is repeated visits for wear of the retentive nylon inserts (BDJ clinical report on two-implant mandibular overdentures, 2024). Across implant overdentures generally, loosening of the attachment components and denture fracture are the most common maintenance events, with repair of a fracture around the implant sitting at the top of the list (systematic review on implant number, PMC3517958). You can't remove it. You can only front-load the lab work so the first failure doesn't arrive early. Reinforcement at the housing zone is the single most useful thing a lab does on a retrofit.

4.6 Picking a Retention Curve

Locator housings ship with a family of inserts, running from lowest retention upward. We seated the lowest-retention inserts for delivery, as the clinician asked. The reasoning is practical:

• A new overdenture user has to learn the seat-and-release motion. Starting on the softest insert makes that easier.
• Reduced hand function and cognitive impairment are real considerations in this patient group — retention that is too tight can make a denture hard to remove, and that is a maintenance problem, not a comfort problem.
• Stepping up is a short chairside change. Stepping down means ordering parts.

Inserts are a maintenance consumable. The systematic review on Locator survival puts the system around 97% at roughly three years, with regular insert replacement required (Locator survival systematic review, PMC7654206). We flagged the maintenance expectation in writing to the clinician so they could set it with the patient. The JADA clinical practice guidelines for implant-borne restorations are specific about what that means: a professional examination at least every six months as a lifelong regimen, cleaning of the prosthesis and the implant components at least twice daily, and removal of a removable restoration while sleeping (JADA clinical practice guidelines on recall and maintenance).

4.7 Balancing the Occlusion Against the Existing Upper

This is where retrofit work is harder than a new build. On a new denture pair you set the plane of occlusion fresh. On a retrofit we have to meet the existing upper denture where it is.

Three steps:

1. Mount both dentures on an articulator using the bite record the clinician sent.
2. Mark the contacts with housings in place and inserts seated. The housings themselves don't change the occlusion, but seating the lower on implants changes how the base rests, and that can shift contacts slightly.
3. Adjust only where needed to re-establish bilateral contact. We touch the lower, not the upper. The clinician told us not to touch the upper, so we don't.

That last line is one we repeat internally on every retrofit. "Preserve the opposing denture" is a hard instruction, not a soft suggestion.

4.8 One Try-In, Then Final

The clinician asked for one try-in. We shipped the processed denture with housings seated and inserts at the softest setting, plus a short sheet listing:

• Which abutment got which housing, per site, with the gingival height we worked to
• The remaining base thickness at each milled seat, so the clinician can see what we did without taking the denture apart
• The insert currently in place, and the next-strongest option that fits this housing
• A suggested recall schedule built on the JADA clinical practice guidelines for implant-borne restorations — professional review at least every six months, twice-daily cleaning, overnight removal

If the try-in flagged anything, we would have run one adjustment cycle before closing the case. On this case the clinician confirmed fit, retention and bilateral occlusion at the first try-in, and we processed the final.

4.9 Turnaround

A retrofit like this moves through our floor on the normal lab cadence, not an expedited one. We are a full-service lab with the complete workflow kept in-house — CAD, milling, implant work, ceramics, removable and QC, around 460 staff across departments, with roughly 55 technicians in Removable Dentures and 80 in Implants. That matters for Locator work in two ways:

• Nothing is subcontracted to a second lab. When a case moves between departments, it moves inside the same building.
• Capacity holds in peak season. In normal months the removable floor runs around 4,000 cases a month; in peak months, around 6,500. Overdenture retrofits sit inside that lane.

We don't publish a universal "X days for every Locator retrofit" figure, because scan quality, clarity on abutment height and the condition of the incoming denture all change what can be finished on day one. For this case the clinician and our case coordinator agreed a delivery window at intake, and we delivered against it.

5. The Finished Build

For a retrofit, "the result" is the wrong word. What matters is whether the finished denture does the job the clinician prescribed. Two things describe it.

5.1 The design goals we worked to

• Passive seat on both abutments. No rocking on the housings when the inserts are not under load.
• Even retention curve. Both sides engage and release together.
• Occlusion preserved against the upper denture. Bilateral contact, no new high spots created by the retrofit.
• Reinforced base where the acrylic was thinned. No new weak point around the housings.
• Clinician-ready documentation. The clinician can read the file and know exactly what was done.

Those are build targets, not claims about the patient's experience. The clinician owns the patient outcome; we own the delivery that lets them do their job.

5.2 What shipped

6. Where This Case Sits in the Research

So a reader can check our footing without leaving the page:

• 2-implant lower overdenture as the accepted standard for the edentulous mandible — prosthetic overview of mandibular overdentures, PMC6196685.
• Two-implant overdentures against new conventional dentures on satisfaction and oral-health-related quality of life — meta-analysis PMC6293838.
• Attachment choice when the opposing arch is a conventional maxillary denture — literature review on mandibular overdentures, PMC10874113.
• Maintenance events (loose attachment components, denture fracture around an implant) — systematic review on implant number, PMC3517958, BDJ clinical report, 2024.
• Locator survival and its maintenance load — systematic review and meta-analysis of overdenture attachments, PMC7654206.
• Recall, cleaning and overnight-removal requirements — JADA clinical practice guidelines.
• Removable versus fixed implant-supported dentures, as used on this page — Cleveland Clinic reference.
• FDA on dental implants, including clearance-versus-approval and the risk list — FDA patient page.

7. Working With Us on a Lower Denture Implants Retrofit

If you run a clinic or a lab and you have a lower denture implants retrofit coming up — Locator pickup, housing seats cut into an existing denture, base reinforcement, occlusion preserved against an existing upper — here is what we need from your end, and what you get from ours.

A few practical notes on how we work, since they come up on every intake:

• All production stays inside our own facilities. We don't subcontract Locator work out.
• We welcome factory visits and video audits at the Shenzhen and Huizhou sites — most clinics do a short video walkthrough before the first case.
• Case coordination is a named person, not a shared inbox. On a retrofit that depends on reading the clinician's intent correctly, that is not a small detail.

If this case shape matches something sitting in your chair, send the scans and the denture and we will tell you what is workable before any production starts.