Consequences of the Loss of Mandibular First Permanent Molars

During the mixed-dentition stage of dental development, dentists may encounter patients with first permanent molars considered to have a poor long-term prognosis. In this situation, extraction of the tooth and space closure or use of the extraction space for future orthodontic treatment should be considered. The aim of this article is to give guidelines about treatment planning for patients who have first molars with a poor prognosis during the mixed-dentition stage. Dent Update 2001; 28: 304-308 Clinical Relevance: Patients may present with carious or severely hypoplastic first permanent molars during the mixed-dentition period of dental development. Extraction should be considered when encountering teeth with a poor long-term prognosis. O R T H O D O N T I C S D.S. Gill, BSc, BDS, FDS RCS, Specialist Registrar in Orthodontics, The Royal London Hospitals NHS Trust, R.T. Lee, BDS, MOrth, DOrth, FDS RCS, Consultant Orthodontist and Clinical Director, The Royal London Hospitals NHS Trust, and C.J. Tredwin, BSc, BDS, General Dental Practitioner, London. he first permanent molar (FPM) has been quoted as being the most caries-prone tooth in the permanent dentition, probably as a result of its early exposure to the oral environment. More than 50% of children over 11 years have some experience of caries in such teeth. With a decline in the caries rate, improvements in restorative techniques and high parental expectations, dentists may consider restoration of FPMs with extensive caries and pulpal symptoms during the mixed-dentition stage. However, heavily restored teeth will enter the restorative cycle and may need to be extracted in later life. Late extraction has restorative implications and may lead to unfavourable occlusal changes if spaces are left unrestored. In such cases, consideration should be given to the extraction of these teeth during the mixed-dentition stage. It is commonly quoted that the FPM is not the ideal tooth to be extracted for orthodontic reasons as space is provided away from the labial segments. Although technically demanding, it is possible to use the extraction space orthodontically for the relief of crowding and overjet reduction with favourable results. The aim of this article is to review the consequences following extraction of FPMs and to give guidelines about treatment planning when extracting these teeth. CONSEQUENCES OF THE LOSS OF MANDIBULAR FIRST PERMANENT MOLARS The ideal time for the loss of the mandibular FPM is before the eruption of the second permanent molar, usually at a chronological age of 8–9 years. The second molar may erupt early and a good contact area relationship can eventually be established with the second premolar. Some distal drift of the premolars can also be expected at this stage, particularly if there is crowding in this region. Richardson reported a tendency for lower incisor crowding to diminish in the first year following the extraction of mandibular FPMs. The overbite also tended to increase in the majority of subjects studied, and this was associated with retroclination of the lower incisors. These changes were found particularly in patients who started with proclined lower incisors and increased overjets. In contrast, Thunold found no increase in overbite in a group of patients who had had four FPMs extracted 25 years previously. Further back in the dental arch, it cannot be said with certainty that loss of the FPMs will relieve posterior crowding with subsequent eruption of third molars in all cases. However, Williams and Hosila found a 90% chance of successful third molar eruption (compared with a 55% chance following extraction of premolars). Similarly, Plint found that most third molars erupted following the loss of the FPMs (with a tendency to early eruption), and most established a good contact area relationship with the second molars.