[Suwon Gwonseon-gu Dentist] An Impacted Wisdom Tooth Can Make the Neighboring Molar Collapse First

Distal-surface decay in the second molar next to an impacted wisdom tooth is reported in the literature at 29.89%.

Written by Dr. Ahn Seong-jin, Chief Director, Yeonhap Dental Clinic · Published Aug. 16, 2026 · Last updated Aug. 30, 2026

This article answers the six questions below in order. · What does an impacted wisdom tooth do to the molar next to it? · Which impacted wisdom teeth are risky for the neighboring molar? · Why does the neighboring molar decay at that particular spot? · What decides whether to extract an impacted wisdom tooth or watch it? · What becomes the problem once the neighboring molar has decayed deeply because of a wisdom tooth? · Which should you choose, crown lengthening or DME?

While an impacted wisdom tooth is being watched, what is actually damaged is often not the wisdom tooth but the second molar in front of it. In a systematic review analyzing 13 studies and 13,788 people, the prevalence of distal-surface decay in the second molar next to an impacted lower third molar is reported at 29.89% (Clin Oral Investig 2024). Not only decay but also periodontal problems appear, and one report observed adjacent-surface periodontitis in 39%.

The meaning of these figures is clear. A wisdom tooth is a tooth you can do without, but the second molar is central to chewing function. The problem is the situation in which, while watching a wisdom tooth, what you end up losing is the more important tooth.

However, this does not mean that every impacted wisdom tooth must be extracted. The literature also shows that the risk differs greatly depending on the angle and depth of the impaction. This is why Yeonhap Dental Clinic does not recommend extraction across the board and first checks the type.

· 연합치과의원은 옆 어금니가 깊게 썩어 경계 확보가 필요하면 치관-치근 비율(뼈 위 치아와 뼈 안 뿌리의 길이 비)과 마진 상태를 보고 치관확장술 또는 DME(잇몸 아래 경계를 레진으로 올리는 방법)를 검토해 크라운으로 마무리합니다.

작성: 연합치과의원 대표원장 안성진

사랑니는 아프지 않은데 앞 어금니를 치료해야 한다는 말을 들으면 당황스러우실 수 있습니다.

[글의 목차]

· 어떤 매복 사랑니가 옆 어금니에 위험한가요?

· 매복 사랑니를 뽑을지 지켜볼지는 무엇으로 정하나요?

· 옆 어금니가 깊게 썩은 뒤에는 무엇이 문제가 되나요?

· 치관확장술과 DME 중 무엇을 택하나요?

앞쪽으로 기울거나 누운 사랑니는 큰어금니 뒷면을 비스듬히 밀고 들어와, 두 치아가 만나는 자리가 잇몸선 근처나 그 아래에 생깁니다. 그 자리에는 칫솔모도 치실도 닿지 않아 충치가 잇몸 아래에서 시작되고, 일반 방사선 사진에서는 사랑니와 겹쳐 보여 초기 병소를 놓치기 쉽습니다.

사랑니는 없어도 되는 치아지만 큰어금니는 씹는 기능의 중심입니다. 사랑니를 지켜보다가 더 중요한 치아를 잃는 상황이 문제입니다.

The risk of decay in the neighboring tooth rises greatly with mesioangular impaction and shallow impaction.

In a study using CBCT, the risk of distal-surface decay in the neighboring second molar differed greatly by impaction type. Mesioangular impaction was reported to raise the risk about 11.22 times, and position A (a shallow impaction in which the occlusal surface of the wisdom tooth is close to the height of the second molar's occlusal surface) about 8.37 times (PMC11626789).

Horizontal impaction is also a risk group. Decay occurred significantly more often when the contact point between the wisdom tooth and the second molar was at or below the cementoenamel junction, and one study concluded that a lower third molar with this feature is worth considering for preventive removal (Med Oral Patol Oral Cir Bucal 2017).

Conversely, a vertical impaction that is completely buried in bone and does not touch the neighboring tooth carries a relatively low risk. This difference is what separates watching an impacted wisdom tooth from extracting it.

Because the contact point where the wisdom tooth meets the molar forms in a place the toothbrush cannot reach.

A wisdom tooth tilted mesially or lying horizontally pushes in at an angle against the back of the second molar. The contact point where the two teeth meet then forms near the gum line or below it, and neither toothbrush bristles nor floss reach that spot. The result is a structure in which food and plaque stay but cleaning cannot happen.

The location is also unfavorable. Distal-surface decay begins on the innermost surface of the mouth and progresses below the gum, so by the time pain appears and it is found, it has often already become quite deep. On ordinary X-rays it overlaps with the crown of the wisdom tooth, so early lesions are easily missed.

This is why Yeonhap Dental Clinic uses 3D CT when evaluating an impacted wisdom tooth. We look not only at the angle and depth of the wisdom tooth and its relationship to the nerve canal, but also at whether the distal surface of the neighboring tooth has already been involved and, if so, how deep it has progressed. This last value later becomes the criterion that decides the treatment direction.

We look at the impaction type and whether the neighboring tooth is involved, and pick out the cases that need preventive extraction.

Yeonhap Dental Clinic does not extract impacted wisdom teeth across the board. For a wisdom tooth that is completely buried and does not touch the neighboring tooth, there are cases where it is better to watch it and check for changes at regular check-ups. Conversely, if any of the conditions below apply, we consider extraction first even without symptoms.

· Mesioangular or horizontal impaction with the contact point at or below the cementoenamel junction

· Decay or bone loss already confirmed on the distal surface of the neighboring second molar

· A history of repeated pericoronitis

· A lesion such as a cyst is present

The criterion for judgment is not the wisdom tooth itself but the prognosis of the second molar. It means we do not make a choice that shortens the life of a more important tooth in an attempt to keep one wisdom tooth.

If we decide to proceed with extraction, we measure the distance to the nerve canal on 3D CT to decide the approach, and if the risk is high, for example when the crown is close to the nerve canal, we refer you to an oral and maxillofacial surgeon. We think it is better to tell you from the start what Yeonhap Dental Clinic can and cannot do.

To place a crown on a margin that has dropped below the gum line, the margin has to be exposed or raised.

If, after the wisdom tooth is extracted, there is no decay on the distal surface of the neighboring tooth, that is the end of it. The problem is when it has already progressed deeply. Once the decay is removed, the boundary of sound tooth structure, the margin, remains below the gum. In this state a crown cannot be made, because impression taking and bonding are possible only when the margin is visible and can be isolated.

There are two methods. Either lower the gum and bone to expose the margin above the gum (gingivectomy or crown lengthening), or raise the margin itself (DME, distal margin elevation).

The cost of the first method is as discussed earlier. As much bone as is reshaped, the part surrounding the root decreases and the crown-to-root ratio becomes unfavorable, and teeth whose ratio became 1:1 after crown lengthening are reported to have the lowest survival at 40% (Patil 2019). The detailed calculation is covered in Crown Lengthening: How Much Bone Should Be Removed?.

The second method, DME, is a procedure in which resin is built up over a deep margin to move the margin position coronally. Because it does not touch the bone, the crown-to-root ratio is not lost, but in exchange the newly built resin boundary becomes the very margin on which the crown will sit.

If the crown-to-root ratio can be tolerated, we choose crown lengthening; if it is unfavorable, we choose DME.

Yeonhap Dental Clinic's order of judgment is as follows. We remove the decay to confirm the margin position and measure the root length and bone height on 3D CT. From this we calculate the root length that would remain if the bone were lowered, and if the crown-to-root ratio is within a range we can tolerate, we secure a tooth margin with gingivectomy or crown lengthening. Conversely, if the ratio is calculated to become very unfavorable, we choose DME, which does not touch the bone.

For DME, after isolating with a rubber dam, we push back the gum and the neighboring tooth with a dedicated wedge (Rhondium DME wedge) to expose the margin, and build up the margin in steps with a flowable resin with high filler content (Clearfil Majesty Flow). The reason for choosing the material this way is that this resin is not merely a filler but becomes the very margin on which the crown will sit. Properties favorable for wear and marginal adaptation are needed.

In the literature, the long-term success rate of DME restorations is reported at 94 to 100%, and there is a study reporting a 96% survival of 197 restorations over 12 years (Bresser). For the periodontal response, there are reports that bleeding on probing increased statistically significantly but the absolute difference was small, probing depth was kept under 4 mm, and neither attachment loss nor radiographic bone loss was observed.

However, these results apply when finishing and polishing quality is secured. A rough resin boundary becomes a plaque-retentive spot, so Yeonhap Dental Clinic spends separate time on marginal polishing after DME. And whichever method is chosen, we finish the final restoration with a crown.

[Key Takeaways]

✓ Distal-surface decay in the second molar next to an impacted wisdom tooth is reported at 29.89%, and mesioangular impaction raises the risk about 11.22 times.

✓ Yeonhap Dental Clinic picks out cases for preventive extraction by the impaction type and whether the neighboring tooth is involved, and monitors completely impacted wisdom teeth that do not touch the neighbor.

✓ When the margin has already become deep, we measure the crown-to-root ratio and choose between crown lengthening and DME, and finish with a crown either way.

The practical test of a consultation is whether the dentist explains the condition of the neighboring molar, not just the wisdom tooth itself.

Yeonhap Dental Clinic, at 230 Geumho-ro, 5th Floor (Cham Clinic Building, Tap-dong), Gwonseon-gu, Suwon, across from Suwon NongHyup Guun Branch (231 Geumho-ro), has held the same location since 2002. Dr. Ahn Seong-jin, Chief Director and Integrated Dentistry specialist, is currently in charge, and you can see how wisdom tooth extraction proceeds in Wisdom Tooth Extraction Information.

[5 Things to Check Before a Wisdom Tooth Consultation]

· Whether the angle and depth of the impaction are explained by type

· Whether the condition of the distal surface of the neighboring molar is checked, not only the wisdom tooth

· Whether the distance to the nerve canal and the depth of involvement of the neighboring tooth are measured on 3D CT

· Whether cases that do not need extraction are also explained

· Whether the plan for restoring the neighboring tooth after extraction is also explained

A wisdom tooth is a tooth you can do without. Yet I have seen cases where, while that wisdom tooth was being watched, what was lost was a large molar that has to last a lifetime. I understand the reluctance to have it pulled. But when I look at a wisdom tooth, I do not look at the wisdom tooth alone. I also look at how many years the tooth in front of it can hold up. And even when it is already late, there are still options. Between the path of cutting bone to expose the margin and the path of leaving the bone and raising the margin, I think my job is to choose the one on which that tooth can last longer.

[References]

Prevalence of distal caries in second molar associated with impacted mandibular third molar and the position and level of impaction: a systematic review and meta-analysis. Clin Oral Investig. 2024. doi:10.1007/s00784-024-06131-1.

Cone-beam computed tomographic investigation of the association between impacted mandibular third molars and the development of distal caries in adjacent second molars in a Chinese population. PMC11626789.

Impacted lower third molars and distal caries in the mandibular second molar. Is prophylactic removal of lower third molars justified? Med Oral Patol Oral Cir Bucal. 2017. PMC5474337.

Patil K, Khalighinejad N, El-Refai N, Williams K, Mickel A. The effect of crown lengthening on the outcome of endodontically treated posterior teeth: 10-year survival analysis. J Endod. 2019;45(6):696-700. PMID 31005334.

Restorative and periodontal outcomes of deep margin elevation in posterior teeth: a systematic review. Cureus. 2025. PMC12716966.

Bresser RA, et al. Up to 12 years clinical evaluation of adhesive indirect restorations with deep margin elevation. J Dent. 2019.

This post was written in accordance with the Korean Medical Service Act and the Ministry of Health and Welfare's medical advertising guidelines, and is intended to provide medical information. It does not guarantee or assert the effect of any particular treatment. The applicable procedures and course may vary depending on the form of the impaction and the condition of the neighboring tooth, so please decide on a diagnosis and treatment direction only after a thorough consultation with your dental team.

🦷 Wisdom tooth extraction information: Yeonhap Dental Clinic wisdom tooth extraction

📍 230 Geumho-ro, 5th Floor (Cham Clinic Building, Tap-dong), Gwonseon-gu, Suwon, Gyeonggi-do

🚕 Across from Suwon NongHyup Guun Branch (231 Geumho-ro) / about 15 minutes by taxi from Suwon Station

🚗 Free parking available in the building

📞 031-293-2207

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🟡 Open since 2002 / Treatment overseen by Dr. Ahn Seong-jin, Chief Director and Integrated Dentistry specialist

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