GP1b - Maintaining Retained Primary Molars in Hypodontia Patients to Reduce Surgical Complexity of Dental Implant Surgery: An Observational Study

Abstract: Bone augmentation for dental implantology is in vogue. Hypodontia patients frequently lack bone volume and quality, so instead maintenance of bone may be in part a neglected detail that requires a refocus. Recent evidence emphasizes the need for careful planning for patients with hypodontia and retained primary molars (RPM).1 Potential implant planning for congenital hypodontia, is complicated by lacking alveolar bone and buccal / lingual concavities.2 Furthermore hypodontia patients presenting with RPM, can have unwanted sequelae of tipping of permanent teeth, over-eruption of opposing teeth, food packing, and prolonged dental and surgical management.

This study aimed to estimate the association between maintaining or extracting retained deciduous molars in hypodontia patients and the surgical complexity to place dental implants.

Material and methods:
A cohort of 650 patients who had dental implants planned in the same multidisciplinary hypodontia clinic and placed in the same oral surgery department over a 10-year period were assessed. Inclusion criteria: Congenital hypodontia patients with a RPM. Exclusion criteria: Patients with a clinical or molecular diagnosis of ectodermal dysplasia and those who had implants placed for reasons other than congenital hypodontia (e.g., post head and neck cancer). Patient- and tooth-specific data including, hypodontia severity, infra-occlusion classification, and gender obtained from clinical records and DPT images. Implant surgery data was obtained from single-operator database and operation notes including: whether immediate placement, one-stage or two-stage surgery undertaken, bone augmentation requirements and implant survival.

Methods of data analysis:
Categorical variables were described as counts and percentages. Nominal data was stratified. Chi-square contingency analyses conducted to assess for statistically significant relationship between maintaining or extracting retained deciduous molars and complexity of implant surgery.

Results:
The study reflects 116 patients, with a total of 273 retained primary molars (RPM), subsequently replaced by dental implants. The majority of RPM (69%) had some degree of infraocclusion. Mean age at implant surgery was 24 years old. Implant survival was 96.4%. Most patients had severe hypodontia (≥6 missing teeth). The most common RPM were lower second primary molars (39%) then upper first primary molars (30%), upper second primary molars (50, 18%) and lower first primary molars (13%).

Outcomes data:
Eighty-one percent of patients had severe hypodontia. Forty-eight RPM were extracted early, all with some degree of infraocclusion. This was significantly associated with the need for grafting to the implant site (chi-squared = 28.01 P < .00001), and whether surgery was one stage or two stage.

Conclusion:
Patients undergoing early extraction required more grafting for their implant surgery than those who had their primary molars retained for longer. Also, those who had their primary molars maintained rather than early extraction had less complex implant surgery. This study supports maintaining submerged deciduous molars so to reduce number of implant operations and bone augmentation required. Further work is required to better understand the patient and service cost implications and bone volume differences between groups.

References
1. N Patel et al. Restorative dentistry clinical decision-making for hypodontia: retained primary molars. British Dental Journal. 2023;235(7):477-482.
2. Orloff et al. Restorative dentistry clinical decision-making for hypodontia: managing missing premolar teeth. British Dental Journal. 2023;235)483-488.