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Abstracts - 23

1. Prophylactic Removal of Impacted Third Molars: Is It Justified? 
2. The unresolved problem of the third molar 
3. Surgical removal of third molars

The unresolved problem of the third molar 

Would people be better off without it?

Background Third molars are teeth that have little functional value and a relatively high rate of associated pain and disease. Their value as part of the dentition of modern people is dubious.

Types of Studies ReviewedThe authors review the evolution, development, morbidity and treatment of third molars. They assess the value of third molars in the 21st century and describe the risks these teeth pose when they develop in the

Conclusions There is a mandate for the dental profession to improve health outcomes and quality of life. The prevention of third molar–related morbidity should be included in dental research efforts. The authors suggest that novel preventive methodologies be developed to alleviate the problems third molars pose. One potential methodology suggested is intentional therapeutic agenesis of this tooth.

Clinical Implications  Prevention of third molar development early in life, even before tooth bud initiation, could
dramatically improve health care outcomes for millions of people.

Prophylactic Removal of Impacted Third Molars: Is It Justified? 
British Journal of Orthodontics, Vol. 26, No. 2, 149-151, June 1999 © 1999 British Orthodontic Society Effectiveness Matters It is the subject of Effectiveness Matters Vol. 3, Issue 2, October 1998 and since the conclusions of this systematic review are so important, I have felt further dissemination to a wider audience was justified. The `housestyle' is in accord with the original publication source on this occasion. Background Removal of third molars wisdom teeth is one of the most common surgical procedures within the UK. In 1994-95 there were over 36,000 in-patient and 60,000 day-care admissions in England for `surgical removal of tooth'. 1 Third molar surgery has been estimated to cost the NHS in England up to £30 million per year, 2 and approximately £20 million is spent annually in the private section. 3 Around 90 per cent of patients on waiting lists for oral and maxillofacial surgery are scheduled for third molar removal. 3 There are wide variations in rates of third molar surgery across the UK. 4,2 There is also some evidence that deprived populations with poor dental health are less likely to have third molars removed than more affluent populations with good dental health. 5,2 However, the reasons for this are complex. Little controversy surrounds the removal of impacted third molars when they cause pathological changes and/or severe symptoms, such as `infection, non-restorable carious lesions, cysts, tumours, and destruction of adjacent teeth and bone'. 6 However, the justification for prophylactic removal of impacted third molars is less certain and has been debated for many years. The October 1998 issue of Effectiveness Matters summaries research evidence evaluating the appropriateness of prophylactic removal of impacted third molars. Several reasons are given for the early removal of asymptomatic or pathology-free impacted third molars, almost all of which are not based on reliable evidence: they have no useful role in the mouth, they may increase the risk of pathological changes and symptoms, and if they are removed only when pathological changes occur, patients may be older and the risk of serious complications after surgery may be greater. On the other hand, the probability of impacted third molars causing pathological changes in the future may have been exaggerated. 3,7 Many impacted or unerupted third molars may eventually erupt normally and many impacted third molars never cause clinically important problems. 8 In addition, third molar surgery is not risk free; the complications and suffering following third molar surgery may be considerable. 9 Therefore, prophylactic removal should only be carried out if there is good evidence of patient benefit. The proportion of third molar surgery, which is carried out prophylactically in asymptomatic patients, is difficult to estimate precisely and depends on the definitions used. A UK survey of 181 consultants, found that 35.1 per cent of 25,001 third molars removed were disease free.10 Other, reliable estimates of prophylactic removal suggest rates of between 20 to 40 per cent, 11,12,13 though rates as low as 4 per cent have been reported. 14 Pathological Changes Associated with Impacted Third Molars There has been no long-term experimental evaluation of prophylactic removal. Therefore, the decision to extract prophylactically depends on an estimate of the balance between the likelihood of the unoperated molars causing pathology in the future, the advantage of earlier versus later surgery, and the risk of surgery in those who would never need extraction. Pericoronitis (inflammation of the gingiva surrounding the crown of a tooth) is the most common indication for third molar sugery, 10 and mainly occurs in adolescents and young adults, but less commonly in older people. 15 A study reported that over 4 years of follow-up, 10 per cent of lower third molars develop pericoronitis. 16 Very few impacted third molars cause dental caries (decay) of second molars, 15 though estimates vary (1-4.5 per cent). 9 Fear of second molar caries is not a justification for prophylactic removal. There is a low incidence (less than 1 per cent) of root resorption of second molars with impacted third molars. 16,17 One review concludes that the risk of second molar root resorption by impacted third molars is low and is likely to occur in younger patients for whom surgery is claimed to be associated with less morbidity. 15 The association between anterior (front) incisor crowding and impacted third molars is not significant and does not warrant the removal of third molars. 18,19,20 Cyst development is very rare and is not an indication for prophylactic removal. 15 The risk of malignant neoplasms arising in a dental follicle is negligible and is not an indication for prophylactic removal. 15 Complications and Risks Following Surgery The potential benefit of avoiding the relatively uncommon risk of pathology associated with leaving impacted third molars in place needs to be considered alongside the risks associated with their removal. Patients should be fully informed of the potential risks and benefits. Common complications following third molar surgery include sensory nerve damage (paraesthesia), dry socket (dry appearance of the exposed bond in the socket accompanied by severe pain and foul odour), infection, haemorrhage, and pain. Rarer complications include severe trismus, oro-antral fistual, buccal fat herniations, iatrogenic damage to the adjacent second molar, and iatrongic mandibular fracture. The rate of sensory nerve damage after third molar surgery has been shown to range from 0 to 20 per cent. 9,15,21,22 The overall rate of dry socket varies from 0 to 35 per cent among studies. 9,23 The risk of dry socket increases with lack of surgical experience and tobacco use, 24 though this does not justify prophylactic removal. Prophylactic Removal: Is It Justified? A recent evaluation of published reviews 19 has concluded that there is little reliable evidence to support prophylactic removal of impacted third molars. Two decision analyses also concluded that, on average, patients' longer term well-being is more likely to be maximized if only those impacted third molars with pathology are removed. 22,25 Two reviews from North America also confirm this conclusion. One acknowledged a lack of reliable evidence to support the prophylactic removal of impacted third molars. 26 The other concluded that `routine prophylactic third molar extraction is unjustifiable'. 15 It showed that impacted third molars in adolescents are most likely to develop pathological indications, while impacted third molars in adults are unlikely to undergo significant pathological changes. This review also indicated that `older patients, for whom third molar extraction is necessary, generally tolerate the procedure well'. Given the lack of reliable evidence, a general anaesthetic for the removal of a symptomatic third molar should not normally be sufficient justification for removing pathology-free third molars at the same time. Risks: pathology versus Surgery In a comparison of the risk of pathological changes in retained third molars and complications after third molar surgery, 15 the rate of complications after removing third molars was 11.8 per cent in youths (age range 12-29) and 21.5 per cent in older age (age range 25-81). In addition, results from several studies showed that the risk of pathological changes in older adults ranges from zero to 12 per cent. Using these figures, it can be calculated that there will be more complications after prophylactic removal of pathology free third molars than after removing only those third molars with pathological changes (see Table 1). For every 100 young people who would undergo prophylactic removal 12 may be expected to suffer from clinically significant complications. Without prophylactic removal, 12 of these 100 people will require surgical removal of third molars at older ages, of whom only three will experience surgical complications. TABLE 1 Number of complications after surgical removal of third molars: a comparison of two strategies These estimates of the risk of leaving impacted third molars and the risks of prophylactically extracting them are necessarily approximate because of the relatively poor quality or research in this area and difference methods used by studies. Dental surgeons will tend to see (and remember) those patients who experience long-term problems with impacted third molars, rather than patients with no complications. The perceived risk of impacted third molars and the benefits of prophylactic removal will therefore tend to be exaggerated. Overall, there appears to be little justification for the removal of pathology-free impacted third molars. Conclusions Third molar surgery rates vary widely across the UK. Around 35 per cent of third molars removed for prophylactic purposes in the UK are disease free. Surgical removal of third molars can only be justified when clear long-term benefit to the patient is expected. It is not possible to predict reliably whether impacted third molars will develop pathological changes if they are not removed. There are no randomized controlled studies to compare the long-term outcome of early removal with retention of pathology- free third molars. In the absence of good evidence to support prophylactic removal, there appears to be little justification for the routine removal of pathology-free impacted third molars. To ensure appropriate treatment, referrals and waiting lists for the surgical removal of third molars should be monitored through a process of audit. Recommendations Research evidence suggests that impacted third molars should not be removed unless pathological changes are evident. Ideally, a long-term rigorous experimental evaluation of prophylactic removal is required. More practically, high quality observational studies in some countries where this practice has not been routine, may shed light on the natural history of impacted third molars. Referrals and waiting lists for the surgical removal of third molars should be monitored through a process of audit (to ensure appropriate treatment). Acknowledgments Article reprinted by kind permission of NHS Centre for Reviews and Dissemination, York. References 1 Department of Health. Hospital Episode Statistics, England: Financial Year 1994-95 Volume 1: Finished Consultant Episodes by Diagnosis and Operatives Procedure. London: DOH, 1996. 2 Landes, D. P. The relationship between dental health and variations in the level of third molar removals experienced by populations. Community Dental Health 1998; 15L 67–71.[Medline] 3 Shepherd, J. P., Brickley, M. Surgical removal of third molars. British Medical Journal 1994; 309: 620–621.[Free Full Text] 4 Toth, B. The Appropriateness of Prophylactic Extraction of Impacted Third Molars. A Review of the Literature. Health Care Evaluation Unit, University of Bristol, 1993. 5 Gilthorpe, M. S., Bedi, R. An exploratory study combining hospital episode statistics with socio-demographic variables, to examine the access and utilisation of hospital oral surgery services. Community Dental Health 1997; 14(4): 209–213.[Medline] 6 NIH. Consensus development conference for removal of third molars. Journal of Oral Surgery 1980; 38: 235-236. 7 Stephens, R. G., Kogon, S. L., Reid, J. A. The unerupted or impacted third molar—a critical appraisal of its pathologic potential. Journal of the Canadian Dental Association 1989; 55(3): 201–207.[Medline] 8 Ahlqwist, M., Grondahl, G. Prevalence of impacted teeth and associated pathology in middle-aged and older Swedish women. Community Dentistry and Oral Epidemiology 1991; 19(2): 116–119.[Medline] 9 Mercier, P., Precious, D. Risks and benefits of removal of impacted third molars. International Journal of Oral and Maxillofacial Surgery 1992; 21: 17–27.[Medline] 10 Worral, S. F., Riden, K., Haskell, R., Corrigan, A. M. UK National Third Molar project: the initial report. British Journal of Oral and Maxillofacial Surgery, 1998; 36(1): 14–18. 11 Lopes, V., Mumenya, R., Feinmann, C., Harris, M. Third molar surgery: an audit of the indications for surgery, post- operative complaints and patient satisfaction. British Journal of Oral and Maxillofacial Surgery 1995; 33: 33–35. 12 Brickley, M., Shepherd, J., Mancini, G. Comparison of clinical treatment decisions with US National Institutes of Health consensus indications for lower third molar removal. British Dental Journal (1993); 185: 102–105. 13 Brickley, M. R., Shepherd, J. P. Performance of a neural network trained to make third-molar treatment-planning decisions. Medical Decision Making 1996; 16(2): 153–160.[Abstract/Free Full Text] 14 Pratt, C. A. M., Hekmat, M., Barnard, J. D. W., Zaki, G. A. Indications for third molar surgery. Journal of the Royal College of Surgeons of Edinburgh 1998; 43(2): 105–108.[Medline] 15 Daley, T. D. Third molar prophylactic extraction: a review and analysis of the literature. General Dentistry 1996; 44(4): 310–320.[Medline] 16 Von Wowern, N., Nielsen, H. O. The fate of impacted lower third molars after the age of 20. A four year clinical follow up. International Journal of Oral and Maxillofacial Surgery 1989; 18(5): 277–280.[Medline] 17 Linqvist, B., Thilander, B. Extraction of third molars in cases of anticipated crowding in the lower jaw. American Journal of Orthodontics 1982; 81(2): 130–139.[Medline] 18 Vasir, N. S., Robinson, R. J. The mandibular third molar and late crowding of the mandibular incisors—a review. British Journal of Orthodontics 1991; 18: 59–66.[Abstract] 19 Song, F., Landes, D. P., Glenny, A. M., Sheldon, T. A. Prophylactic removal of impacted third molars: an assessment of published reviews. British Dental Journal 1997; 182(9): 339–346.[Medline] 20 Harradine, N. W. T., Pearson, M. H., Toth, B. The effect of extraction of third molars on late lower incisor crowding: a randomised controlled trial. British Journal of Orthodontics 1998; 25: 117–122.[Abstract] 21 Carmichael, F. A., McGowan, D. A. Incidence of nerve damage following third molar removal: a West of Scotland Oral Surgery Research Group study. British Journal of Oral and Maxillofacial Surgery 1992; 30(2): 78–82. 22 Brickley, M., Kay, E., Shepherd, J. P., Armstrong, R. A. Decision analysis for lower-third-molar surgery. Medical Decision Making 1995; 15(2): 143–151.[Abstract/Free Full Text] 23 Chiapasco, M., Crescentini, M., Romanoni, G. Germectomy or delayed removal of mandibular impacted third molars: the relationship between age and incidence of complications. Journal of Oral and Maxillofacial Surgery 1995; 53(4): 418–422.[Medline] 24 Larsen, P. E. Alveolar osteitis after surgical removal of impacted mandibular third molars. Identification of the patient at risk Oral Surgery, Oral Medicine, Oral Pathology 1992; 73(4): 393–397.[Medline] 25 Tullock, J. F., Antczak Bouckoms, A. A. Decision analysis in the evaluation of clinical strategies for the management of mandibular third molars. Journal of Dental Education 1987; 51(11): 652–660.[Abstract] 26 ECRI. Removal of third Molars. Executive Briefings, Health Technology Assessment Information Service 1994. BMJ 1994;309:620-621 (10 September) Editorials Surgical removal of third molars The surgical removal of teeth is one of the four surgical operations included in both top 10 day case and inpatient NHS procedures for England and Wales.1 The other three procedures, for 1989-90, were endoscopic operations on the upper gastrointestinal tract and bladder and evacuation of the contents of the uterus. Surprisingly, in the last year for which statistics are available (1989-90) more than twice as many people (60 000) were admitted for the surgical removal of teeth as were treated as day cases (28 000). For inpatient procedures, the surgical removal of teeth was ninth in frequency behind vasectomy. The surgical removal of third molars (wisdom teeth) accounted for 70% of these procedures in 1989-90. In addition, 67 000 people had their third molars removed by dental practitioners in the general dental service and 22 000 had their third molars removed in the private sector. The total cost of third molar removal in the NHS in 1989-90 was estimated as pounds sterling 23.3m and in the year ended 30 June 1992 was pounds sterling 22m in the private sector.2 In the hospital service, patients waiting for third molar removal account for up to 90% of patients on waiting lists in oral and maxillofacial surgery.3 Although patient throughput has increased year on year since 1985, in 1990 the oral and maxillofacial surgery waiting lists remained among the longest of any surgical specialty. Despite the very large number of third molars that are being removed, audit suggests that rates of surgical intervention could be reduced and that more rational decision making is needed.2,4 Although prophylactic removal has previously been criticised5 and the cost-benefit ratio of this procedure is very poor,6 little evidence exists of a link between levels of morbidity and intervention. Wide small area variation in operation rates for the South West Regional Health Authority has been reported,2 and recent comparisons of treatment decisions with National Institutes of Health consensus criteria for intervention have shown that about a fifth of patients not meeting these criteria were nevertheless scheduled for surgery.4 A recent literature review concluded that "prophylactic surgery is not an appropriate management strategy for third molars."6 The wholesale removal of unerupted teeth seems as inappropriate as the wholesale removal of tonsils and adenoids. In terms of health gain, the scales are loaded against intervention even in the presence of mild pericoronitis (inflammation around the crown).6 Previously, prophylactic surgery has been justified on the basis that third molars have no role in the mouth, notwithstanding that few people would contemplate the prophylactic removal of their appendix, which, unlike many unerupted third molars, communicates with the alimentary tract throughout life. Prophylactic removal has also been justified on the basis that unerupted teeth contributed to facial pain and even that the presence of an unerupted tooth weakens the lower jaw such that it is likely to fracture; no objective evidence exists to substantiate these assertions. No reliable evidence is available on trends in the incidence and severity of infections associated with the eruption of third molars, but the number of third molars surgically removed by family dental practitioners has increased by 30% since 1988. Good reasons exist why the number of impacted unerupted teeth are increasing, including improved dental health leading to fewer extractions of standing teeth and therefore decreased space for third molars to erupt. Surveillance has also improved, as more people now attend for dental treatment; payment by capitation has been introduced into dentistry, and the use of panoral x ray machines is increasing. The indications for removing third molars was the subject of a National Institutes of Health consensus conference held in the United States in 1979.7 The consensus criteria for surgical intervention were recurrent pericoronitis, caries not amenable to restorative measures, dentigerous cyst, internal or external resorption, and periodontal disease to which the third molar was contributing. Overall, pericoronitis is the reason for intervention in about one fifth of removals,8 though a study of more than 16 000 lower third molars showed that only 8% had been removed for this problem.9 Recent evidence suggests that the teeth at most risk are partially erupted, vertically placed mandibular third molars. The prevalence of periodontitis associated with third molars is also low - reportedly about 5% in studies of 1200 and 1800 impacted third molars.10 In relation to resorption of the adjacent second molar, prevalence has been estimated at about 2%. Crowding of anterior teeth has previously been attributed, at least in part, to the eruption of third molars, but recent findings and reviews all strongly suggest no causal link.11 The prevalence of cystic change has been found to be about 2-4%. There are many reports of an association between facial pain and the presence of unerupted third molars, though there is no evidence of a causal link. There is enormous potential for mistaken diagnoses and unnecessary surgery: regular dental surveillance, both clinical and radiological, is the cornerstone of modern preventive dentistry, and facial pain is a common complaint, particularly in young adults. Radiological surveys of the mouth and jaws have shown that about one in five people in their 30s have at least one unerupted third molar12 and that these can remain in situ throughout life without pathological change. The complications associated with the removal of unerupted third molars should not be underestimated. The surgery entails incision, stripping of periosteum, bone and tooth removal, and suturing. Pain, swelling, and trismus are almost universal after this procedure, and the incidence of both inferior dental and lingual nerve damage is high. After surgical removal of lower third molars, 5-15% of patients suffer some numbness of the anterior two thirds of tongue and ipsilateral lower lip, and lingual numbness is permanent in about 0.5% of cases.13 Surprisingly, until very recently no studies of the preferences of patients have been carried out. Recent evidence, however, suggests that the disadvantages and complications of surgery are generally considered by patients as more serious than those of non-intervention. In any event, the prophylactic removal of third molars should be abandoned. If surgery was carried out only where National Institutes of Health consensus criteria existed then surgical morbidity and costs would be reduced substantially. J P Shepherd, M Brickley Department of Health. Hospital Episode Statistics (1990). London: DoH, 1993. Toth B. The appropriateness of prophylactic extraction of impacted third molars. Bristol: Bristol Health Care Evaluation Unit, University of Bristol, 1993. South West Regional Health Authority. Demand for elective admission for selected procedures, 1991. Bristol: SW RHA, 1992. Brickley MR, Shepherd JP, Mancini G. Comparison of clinical treatment decisions with US National Institutes of Health consensus indications for lower third molar removal. Br Dent J 1993;175:102-5. [Medline] Bramley P. Sense about wisdoms. J R Soc Med 1981;74:867-9. [Medline] Mercier P, Precious D. Risks and benefits of removal of impacted third molars. J Oral Maxillofac Surg 1992;21:17-27. National Institutes of Health. Consensus development conference for removal of third molars. Journal of Oral Surgery 1980;38:235-6. [Medline] Nordenram A, Hultin M, Kieldman O, Ramstrom B. Indications for surgical removal of third molars: study of 2630 cases. Swed Dent J 1987;11:23-9. [Medline] Osborn T, Frederickson B, Small I, Torgerson T. A prospective study of complications related to mandibular third molar surgery. J Oral Maxillofac Surg 1985;43:767-9. [Medline] Kugelberg CF. Periodontal healing two and four years after impacted lower third molar surgery. A comparative retrospective study. Int J Oral Maxillofac Surg 1990;19:341-5. [Medline] Ades A, Joondeph D, Little R, Chapkes M. A long term study of the relationship of third molars to changes in the mandibular dental arch. Am J Orthod Dentofacial Orthop 1990;97:323-35. [Medline] Hugoson A, Kugelberg CF. The prevalence of third molars in a Swedish population. An epidemiological study. Community Dent Health 1988;5:121-38. [Medline] Blackburn CW, Bramley PA. Lingual nerve damage associated with removal of lower third molars. Br Dent J 1989;167:103-7. [Medline]
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