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Maintaining retained infra-occluded primary molars in hypodontia patients to reduce surgical complexity of dental implant surgery: a retrospective study

British Dental Journal (2025)Cite this article

Abstract

Introduction When a permanent premolar is absent, the ultimate treatment goal is often replacement with an implant-retained restoration. Before this, the retained primary molar (RPM) may undergo infra-occlusion and be extracted early. This retrospective study looked at the influence of early extraction or maintenance and restoration of RPMs on the requirement for grafting in the implant site.

Patients and methods From a large cohort of implant recipients, 273 RPMs from 84 patients were replaced with implants and the interventions before implant placement recorded.

Results The most common RPM was the lower second primary molar and 189 (69%) had some degree of infra-occlusion. Additionally, 47 (17%) of RPMs were extracted early, and this was significantly associated with the need for grafting at the implant site (p <0.00001). Sinus lifts were not associated with early RPM extraction. Also, 25 infra-occluded RPMs were restored with onlays, but this had no ultimate influence on grafting at the implant site.

Conclusion Maintenance of an RPM with no permanent successor, even when infra-occluded, has a significant beneficial effect on preserving bone volume for implant placement.

Key points

  • If the planning decision is that space closure is not possible and a retained primary molar be kept, the developing dentition should be monitored for infra-occlusion and to intercept any tipping or over-eruption by restoring the primary molar.

  • Extraction of a retained primary molar before implant placement can complicate the implant process in adulthood.

  • Even if infra-occluded, maintaining the retained primary molar until implant placement can preserve the bucco-lingual width and bone volume, which can reduce the need for grafting and bone augmentation.

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Data availability

Data are available on request from the corresponding author.

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Acknowledgements

With acknowledgement and thanks to H. Muhsin for data collection. Radiograph figure 1b, with kind permission from Dr Hussam Lone.

Author information

Authors and Affiliations

  1. Post-CCST in Paediatric Dentistry, King´s NHS Trust, UK

    Sara Chapman

  2. Consultant in Paediatric Dentistry, Guy´s and St Thomas´ NHS Trust, UK

    Mike Harrison

  3. Specialty Registrar in Oral Surgery, Guy´s and St Thomas´ NHS Trust, UK

    Alex Orchard

  4. Consultant in Oral Surgery, Guy´s and St Thomas´ NHS Trust, UK

    Jerry Kwok

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  1. Sara Chapman
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  2. Mike Harrison
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  3. Alex Orchard
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  4. Jerry Kwok
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Contributions

SC: first author, data collection, data analysis and preparation of manuscript. MH: data collection, data analysis and preparation of manuscript. AO: data collection and preparation of manuscript. JK: provision of data and preparation of manuscript.

Corresponding author

Correspondence to Sara Chapman.

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The authors declare no conflicts of interest. Ethical approval and consent was not necessary, as this was a retrospective review, where no identifiable patient information was used and no patients were contacted.

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Chapman, S., Harrison, M., Orchard, A. et al. Maintaining retained infra-occluded primary molars in hypodontia patients to reduce surgical complexity of dental implant surgery: a retrospective study. Br Dent J (2025). https://doi.org/10.1038/s41415-024-8116-y

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  • DOI: https://doi.org/10.1038/s41415-024-8116-y

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