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Mandibular third molars: oral surgeons’ assessment of the indications for removal
British Journal of Oral and Maxillofacial Surgery (1999) 37, 440–443 © 1999 The British Association of Oral and Maxillofacial Surgeons
B BR RIIT TIIS SH H JJO OU UR RN NA AL L O OF F O OR RA AL L
& &M MA AX XIIL LL LO OFA FAC CIIA AL LS SU UR RG GE ERY RY
Mandibular third molars: oral surgeons’ assessment of the indications for removal R. Liedholm,* K. Knutsson,† L. Lysell,‡ M. Rohlin§ *Lecturer, Department of Oral Surgery; Faculty of Odontology Malmö University, Malmö; †Research Associate, Department of Oral Radiology; Faculty of Odontology, Malmö University; ‡Head, Department of Oral Surgery, Central Hospital, Kristianstad; §Professor, Head, Department of Oral Radiology, Faculty of Odontology, Malmö University, Malmö, Sweden SUMMARY. The aim was to examine oral surgeons’ assessment of the indications for removal of mandibular third molars. Questionnaires were distributed to seven oral and maxillofacial surgery clinics. The oral surgeons were asked to record whether or not there was associated disease. Three other factors were recorded: patient’s age, and angular position and extent of eruption of the molars. The strength of the indication for removal was rated on a visual analogue scale (VAS) where 0= weakest and 100= strongest indication for removal. The results were based on data from 666 molars: 118 (18%) had no disease, 465 (70%) had one associated disease, 77 (11%) had two and 6 (1%) had three. The indication for removal as expressed by the mean VAS for molars with no disease was assessed to be weaker (P<0.05) than that for molars with one, two, or three diseases. The only factor that influenced the indication for removal in molars with no disease was the patient’s age. results of this study indicated that the dentists had different thresholds, at which they should or should not recommend removal. We assume that molars that were to be removed in oral and maxillofacial surgery clinics, might also have different indications, so our hypotheses about oral surgeons’ assessments of mandibular third molars that were to be removed were that the indications for removal of molars with associated disease would differ from those of molars that were without disease; and that the age of the patient, and the angular position and extent of eruption of molars that were without disease would influence the indications for removal.
INTRODUCTION Removal of third molars is the most common surgical procedure in dentistry. The proportion of third molars that are removed when no disease is present is reported to be between 18% and 40%.1–3 Prophylactic third molar surgery is based on the concept of minimizing the future risk of disease and surgical morbidity in older patients.4 This policy has, however, been questioned by Tulloch et al.5 and Brickley et al.6 To reduce unnecessary expenditure on health and to maximize health gains to patients, they suggested that it was more rational to remove only those third molars with associated disease. The quality of health care is determined by two main factors: the reliability of the judgements and decisions that govern how we act and the skill with which those actions are carried out.7 The importance of ensuring the quality of treatment is well understood by dentists. In contrast, the profession has done less to develop and evaluate its judgemental and decision-making processes. If we want to improve these processes, we need to study how dentists think and observe and how they respond to well-defined tasks. When it comes to the decision about whether to remove asymptomatic mandibular third molars, general dental practitioners8 and oral surgeons9 have shown wide variations in the number of molars that they propose to remove. This decision, which is dichotomous (to remove or not to remove) involves thinking about which molars will develop disease. The reason may vary in strength, and may be quantified.10 To elucidate the strength of the reasoning, we quantified dentists’ perceptions of the strength of the indication for prophylactic removal of mandibular third molars using a visual analogue scale (VAS).11 The
PATIENTS AND METHODS Participating clinics Seven oral and maxillofacial surgery clinics in the National Health Service in the southern region of Sweden were asked to participate. More than 95% of patients referred for specialist oral and maxillofacial surgical care in this region are treated in those clinics. Two to five certified specialists work in each clinic.
Patients and questionnaire Questionnaires were distributed to be completed for 100 consecutive patients in each clinic before removal of mandibular third molars. From four clinics, fewer than 100 questionnaires were returned, so data about 666 patients were available for analysis. The angular position of each mandibular third molar was recorded as vertical, mesioangular, distoangular, or horizontal, 440
Mandibular third molars: indications for removal
441
Table 1 – Number of surgically removed mandibular third molars (n=666) that were removed prophylactically or had one, two, or three diseases and the oral surgeons’ assessment of the indication for removal expressed in mean and median VAS (0= weak and 100= strong indication for removal). No. of molars
VAS (mm) Mean (SD)
VAS (mm) Median (Range)
118 548 465 77 6
44 (27) 76 (18) 75 (18) 78 (17) 91 (5)
39 (0–100) 79 (2–100) 78 (2–100) 82 (33–100) 92 (83–96)
Removed prophylactically Removed due to disease: One disease Two diseases Three diseases
Table 2 – Difference between mean VAS based on the oral surgeons’ assessment of the indication for removal of different groups of molars compared with one another in pairs. The molars were removed prophylactically or had one, two, or three diseases respectively Groups of molars Three compared with two diseases Three compared with one disease Three compared with no disease Two compared with one disease Two compared with no disease One compared with no disease
Difference between mean indices 12 15 47* 3 35* 31*
* P<0.05
according to the criteria laid down by Winter.12 The extent of eruption was classified as: (1) fully erupted; (2) partially covered by soft tissue; (3) completely covered by soft tissue; and (4) completely covered by bone tissue. Criteria for the angular position and extent of eruption were described in each questionnaire. The age and sex of the patient were also to be recorded. The oral surgeons were asked to record whether or not there was a disease of the mandibular third molar. Up to six specific diseases (pericoronitis, periodontitis, caries, root resorption, cyst, tumor), as described in Knutsson et al.3 could be recorded, with an option to record any other, as well. The oral surgeons were asked to complete the questionnaire before operation. When necessary, the recordings were supplemented with operative findings or histopathological details of the biopsy specimen. The last variable to be recorded was the indication for the removal assessed on a VAS, the 0 and 100 endpoints of which indicated the weakest and strongest indications for removal, respectively.
Analysis The response on each VAS was measured to the nearest millimetre. The data were analysed using the SPSS (Statistical Package for the Social Sciences) program. The differences between the mean VAS of the groups of molars with no disease and with one or more diseases, respectively, were tested using one-way analysis of variance (ANOVA). If any of the factors – age, angular position, extent of eruption, and/or the interaction
between the factors – had a significant influence on the assessment on the indications for removal of molars without disease, it was tested using three-way ANOVA. The level of significance was set at P=0.05. The coefficient of determination (R2) indicated the extent to which the variation in the assessment of the indication for removal was explained by the three factors and their interactions in molars without disease. Overall the level of significance was set at P=0.05.
RESULTS Patients, and clinical state of molars The results were based on the data from 666 mandibular third molars (one molar per patient). The mean age of the patients was 29 years (range 15–80). Four hundred and seventy one (71%) of the patients were aged between 15 and 29 years. Three hundred and fifty (53%) of the patients were female. One hundred and eighteen molars (18%) showed no disease and 548 molars (82%) did. In 465 molars one disease was recorded, in 77 two, and in six molars three (Table 1). In patients aged 50 or more, all third molars were associated with some disease. Three hundred and ninety nine (60%) of the removed molars were partially covered by soft tissue, 154 (23%) were completely covered by soft tissue, only 32 (5%) were completely covered by bone tissue and 81 (12%) were fully erupted, i.e. not impacted. About one-third of all molars removed, 221, were in a mesioangular position, followed by vertical 191 (29%), distoangular 139 (21%) and horizontal 115 (17%).
Oral surgeons’ assessment of the indications for removal expressed in the VAS The assessment of the indication varied substantially – between 0 and 100 – for molars without disease (Table 1). The SD was higher for this group of molars compared with those with some associated disease. The mean VAS for removal of molars without disease was significantly lower than that for molars with associated disease (Table 2). The differences between the mean VAS for molars with one compared with two or three diseases were not significant. Table 3 shows the number of molars without disease and the mean and median VAS according to:
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British Journal of Oral and Maxillofacial Surgery
Table 3 – Mandibular third molars that were removed prophylactically. Number of removed molars (n=118) in patients of different agegroups and molars of different angular positions and extent of eruption, and oral surgeons’ assessment of the indication for removal expressed as mean and median indication on VAS (0= weak and 100= strong indication for removal) No. of molars
VAS (mm) Mean (SD)
VAS (mm) Median (Range)
36 70 10 2
47 (27) 43 (26) 27 (18) 92 (11)
50 (3–91) 38 (0–98) 24 (2–58) 92 (84–100)
21 60 7 30
46 (26) 44 (28) 45 (33) 43 (26)
46 (10–98) 37.5 (0–100) 27 (7–93) 36.5 (4–95)
6 45
40 (27) 45 (26)
36.5 (11–80) 46 (7–98)
49
44 (24)
38 (0–95)
18
42 (36)
30 (0–100)
Age-group (years) 15–19 20–29 30–39 40–49 Angular position Vertical Mesioangular Distoangular Horizontal Extent of eruption Fully erupted Partially covered by soft tissue Completely covered by soft tissue Completely covered by bone tissue
patients’ age-group; angular positions; and extent of eruption of the molars. Considering age-group, the highest mean and median VAS were given for two patients in the age-group 40–49; both the molars were removed before orthognathic surgery. The mean VAS were comparable for different angular positions and different extent of eruption, but presented a slightly higher variation in median VAS. Excluding the two oldest patients, the patients’ age was the only factor that had a significant effect on the assessment of the indication (P< 0.05) for molars without disease, so the indication was highest for patients of the youngest agegroup and lowest for patients of the oldest age-group. The coefficient of determination (R2) was 0.20 for molars without disease, i.e. the mean proportion of the variation explained by the three factors and the interaction between the factors that influenced the surgeons’ assessment of the indication for removal was 20%.
DISCUSSION In decision-making, we judge whether to act or not – in this case, whether to remove or not to remove a mandibular third molar. Even when we choose an action, there will be the question of how certain we are that the action was correct. In addition to the VAS as used in the present study, receiver operating characteristics (ROC) analysis has been used to study practitioners’ certainty in decision making about third molar removal.13 The results of studies of decision making in endodontics have shown that clinicians do not approach evaluation of treatment as clear-cut but rather operate along a continuum.14 Although the oral surgeons removed all the molars, they gave molars without disease significantly weaker
mean indications than molars with disease. In one sense, this might reflect the surgeons’ doubts about the prophylactic removal of mandibular third molars. Assessments of the indications for removal of molars without disease covered a wide range, between 0 and 100, probably related to the surgeons’ predicted risk of the development of a disease. This is supported by the results of a previous study on dentists’ judgements about the removal of asymptomatic mandibular third molars.15 This study showed that there was a good correlation between each dentist’s indications for removal of a molar and the predicted risk of the development of disease. This judgemental behaviour – the process of inference that precedes a decision – as assessed with the VAS, might indicate the oral surgeons’ limited knowledge about whether or not the third molars would develop disease. This variation in judgemental behaviour can be expected as the natural history of the mandibular third molar is unknown and reported evidence about which molars will develop disease. Of the three factors analysed, the patient’s age was the only one that influenced the oral surgeons’ assessment of the indications in molars without disease. The oral surgeons did not discriminate between molars in different eruptive states or angular positions. Reported evidence3 shows that molars that are partly covered by soft tissue have a 22–34 times higher risk of developing disease than those at other stages of eruption. Molars that are completely covered by soft tissue and molars covered by bone tissue have about an equal risk of developing a disease.3 Distoangular molars have a 5–12 times higher risk of developing a disease than those in other angular positions.3 Despite this evidence, the coefficient of determination for molars without disease was rather low (0.20), and was explained by the three factors – patient’s age, and
Mandibular third molars: indications for removal
angular and eruptive position of the molar. In addition to the patient’s age, other factors such as oral hygiene, and the patient’s degree of caries and periodontitis may have influenced the oral surgeon’s judgement. Another explanation for the low values of R2 might be a lack of cognitive control16 – that means that the oral surgeons were not able to make judgements according to their policy. They might have had problems translating the complexity of the judgement into an assessment on the VAS. The results of this study indicate that there was an awareness among the oral surgeons that prophylactic removal of mandibular third molars could be questioned. When clinicians make their judgements and decisions about treatment they have to deal with the uncertainty and uniqueness of each individual patient.15 We think that greater attention should be paid to the knowledge on which one’s judgements are based. With this study, we hope to increase oral surgeons’ interest in the judgements and decisions that precede the treatment of third molars. Acknowledgement This project was supported by grants from the Swedish Medical Research Council (grant 11647) and the Faculty of Odontology, Malmö University, Sweden.
443
7. Eddy DM. Medical decision making: from theory to practice. Anatomy of decision. J Am Dent Assoc 1990; 263: 441–443. 8. Knutsson K, Brehmer B, Lysell L, Rohlin M. General dental practitioners’ evaluation of the need for extraction of asymptomatic mandibular third molars. Community Dent Oral Epidemiol 1992; 20: 347–350. 9. Knutsson K, Brehmer B, Lysell L, Rohlin M. Asymptomatic mandibular third molars: oral surgeons’ judgement of the need for extraction. J Oral Maxillofac Surg 1992; 50: 329–333. 10. Baron J. What is thinking? In: Baron J, ed. Thinking and deciding, 2nd edn. Cambridge: Cambridge University Press, 1994; 3–15. 11. Lysell L, Brehmer B, Knutsson K, Rohlin M. Rating the preventive indication for mandibular third molar surgery. The appropriateness of the visual analogue scale. Acta Odontol Scand 1995; 53: 60–64. 12. Winter GB, ed. Principles of Exodontia as Applied to the Impacted Third Molar. St Louis: American Medical Books, 1926. 13. Brickley M, Kay E, Shephard JP. Public health aspects of third molar surgery. The effect of surgeons’ treatment thresholds on efficiency and effectiveness. Community Dent Health 1995; 12: 70–76. 14. Kvist T, Reit C, Esposito M et al. Prescribing endodontic retreatment: towards a theory of dentist behaviour. Int Endod J 1994; 27: 285–290. 15. Knutsson K, Brehmer B, Lysell L, Rohlin M. Mandibular third molar as mediated by three cues. Dentists’ treatment decisions on asymptomatic molars compared with molars associated with pathologic conditions. Acta Odontol Scand 1997; 55: 372–377. 16. Brehmer A, Brehmer B. What have we learned about human judgement from thirty years of policy capturing? In: Brehmer B, Joyce CRB, ed. Human judgement. The SJT view. Amsterdam: Elsevier, 1988: 75–114.
REFERENCES 1. Nordenram Å, Hultin M, Kjellman O, Ramström G. Indication for surgical removal of the mandibular third molar. Swed Dent J 1987; 11: 23–29. 2. Lysell L, Rohlin M. A study of indications used for removal of the mandibular third molar. Int J Oral Maxillofac Surg 1988; 17: 161–164. 3. Knutsson K, Brehmer B, Lysell L, Rohlin M. Pathosis associated with mandibular third molars subjected to removal. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1996; 82: 10–17. 4. Hipp BR. The management of third molar teeth. Oral Maxillofac Surg Clin North Am 1993; 5: 77–85. 5. Tulloch CJF, Antczak-Bouckoms AA, Ung N. Evaluation of the costs and relative effectiveness of alternative strategies for the removal of mandibular third molars. Int J Technol Assess Health Care 1990; 6: 505–515. 6. Brickley M, Kay E, Shepherd JP, Armstrong RA. Decision analysis for lower-third-molar surgery. Med Decis Making 1995; 15: 143–151.
The Authors R. Liedholm DDS Lecturer, Department of Oral Surgery K. Knutsson DDS, Odont Dr Research Associate, Department of Oral Radiology M. Rohlin DDS, Odont Dr Professor, Head, Department of Oral Radiology, Faculty of Odontology, Malmö University, Malmö, Sweden L. Lysell DDS, Odont Dr Head, Department of Oral Surgery, Central Hospital, Kristianstad, Sweden Correspondence and requests for offprints to: Dr Rolf Liedholm, Department of Oral Surgery, Faculty of Odontology, Malmö University, 214 21 Malmö, Sweden. Tel: + 46 40 322000; Fax: + 46 40 322046 Paper received 9 February 1998 Accepted 17 March 1998
B BR RIIT TIIS SH H JJO OU UR RN NA AL L O OF F O OR RA AL L
& &M MA AX XIIL LL LO OFA FAC CIIA AL LS SU UR RG GE ERY RY
Mandibular third molars: oral surgeons’ assessment of the indications for removal R. Liedholm,* K. Knutsson,† L. Lysell,‡ M. Rohlin§ *Lecturer, Department of Oral Surgery; Faculty of Odontology Malmö University, Malmö; †Research Associate, Department of Oral Radiology; Faculty of Odontology, Malmö University; ‡Head, Department of Oral Surgery, Central Hospital, Kristianstad; §Professor, Head, Department of Oral Radiology, Faculty of Odontology, Malmö University, Malmö, Sweden SUMMARY. The aim was to examine oral surgeons’ assessment of the indications for removal of mandibular third molars. Questionnaires were distributed to seven oral and maxillofacial surgery clinics. The oral surgeons were asked to record whether or not there was associated disease. Three other factors were recorded: patient’s age, and angular position and extent of eruption of the molars. The strength of the indication for removal was rated on a visual analogue scale (VAS) where 0= weakest and 100= strongest indication for removal. The results were based on data from 666 molars: 118 (18%) had no disease, 465 (70%) had one associated disease, 77 (11%) had two and 6 (1%) had three. The indication for removal as expressed by the mean VAS for molars with no disease was assessed to be weaker (P<0.05) than that for molars with one, two, or three diseases. The only factor that influenced the indication for removal in molars with no disease was the patient’s age. results of this study indicated that the dentists had different thresholds, at which they should or should not recommend removal. We assume that molars that were to be removed in oral and maxillofacial surgery clinics, might also have different indications, so our hypotheses about oral surgeons’ assessments of mandibular third molars that were to be removed were that the indications for removal of molars with associated disease would differ from those of molars that were without disease; and that the age of the patient, and the angular position and extent of eruption of molars that were without disease would influence the indications for removal.
INTRODUCTION Removal of third molars is the most common surgical procedure in dentistry. The proportion of third molars that are removed when no disease is present is reported to be between 18% and 40%.1–3 Prophylactic third molar surgery is based on the concept of minimizing the future risk of disease and surgical morbidity in older patients.4 This policy has, however, been questioned by Tulloch et al.5 and Brickley et al.6 To reduce unnecessary expenditure on health and to maximize health gains to patients, they suggested that it was more rational to remove only those third molars with associated disease. The quality of health care is determined by two main factors: the reliability of the judgements and decisions that govern how we act and the skill with which those actions are carried out.7 The importance of ensuring the quality of treatment is well understood by dentists. In contrast, the profession has done less to develop and evaluate its judgemental and decision-making processes. If we want to improve these processes, we need to study how dentists think and observe and how they respond to well-defined tasks. When it comes to the decision about whether to remove asymptomatic mandibular third molars, general dental practitioners8 and oral surgeons9 have shown wide variations in the number of molars that they propose to remove. This decision, which is dichotomous (to remove or not to remove) involves thinking about which molars will develop disease. The reason may vary in strength, and may be quantified.10 To elucidate the strength of the reasoning, we quantified dentists’ perceptions of the strength of the indication for prophylactic removal of mandibular third molars using a visual analogue scale (VAS).11 The
PATIENTS AND METHODS Participating clinics Seven oral and maxillofacial surgery clinics in the National Health Service in the southern region of Sweden were asked to participate. More than 95% of patients referred for specialist oral and maxillofacial surgical care in this region are treated in those clinics. Two to five certified specialists work in each clinic.
Patients and questionnaire Questionnaires were distributed to be completed for 100 consecutive patients in each clinic before removal of mandibular third molars. From four clinics, fewer than 100 questionnaires were returned, so data about 666 patients were available for analysis. The angular position of each mandibular third molar was recorded as vertical, mesioangular, distoangular, or horizontal, 440
Mandibular third molars: indications for removal
441
Table 1 – Number of surgically removed mandibular third molars (n=666) that were removed prophylactically or had one, two, or three diseases and the oral surgeons’ assessment of the indication for removal expressed in mean and median VAS (0= weak and 100= strong indication for removal). No. of molars
VAS (mm) Mean (SD)
VAS (mm) Median (Range)
118 548 465 77 6
44 (27) 76 (18) 75 (18) 78 (17) 91 (5)
39 (0–100) 79 (2–100) 78 (2–100) 82 (33–100) 92 (83–96)
Removed prophylactically Removed due to disease: One disease Two diseases Three diseases
Table 2 – Difference between mean VAS based on the oral surgeons’ assessment of the indication for removal of different groups of molars compared with one another in pairs. The molars were removed prophylactically or had one, two, or three diseases respectively Groups of molars Three compared with two diseases Three compared with one disease Three compared with no disease Two compared with one disease Two compared with no disease One compared with no disease
Difference between mean indices 12 15 47* 3 35* 31*
* P<0.05
according to the criteria laid down by Winter.12 The extent of eruption was classified as: (1) fully erupted; (2) partially covered by soft tissue; (3) completely covered by soft tissue; and (4) completely covered by bone tissue. Criteria for the angular position and extent of eruption were described in each questionnaire. The age and sex of the patient were also to be recorded. The oral surgeons were asked to record whether or not there was a disease of the mandibular third molar. Up to six specific diseases (pericoronitis, periodontitis, caries, root resorption, cyst, tumor), as described in Knutsson et al.3 could be recorded, with an option to record any other, as well. The oral surgeons were asked to complete the questionnaire before operation. When necessary, the recordings were supplemented with operative findings or histopathological details of the biopsy specimen. The last variable to be recorded was the indication for the removal assessed on a VAS, the 0 and 100 endpoints of which indicated the weakest and strongest indications for removal, respectively.
Analysis The response on each VAS was measured to the nearest millimetre. The data were analysed using the SPSS (Statistical Package for the Social Sciences) program. The differences between the mean VAS of the groups of molars with no disease and with one or more diseases, respectively, were tested using one-way analysis of variance (ANOVA). If any of the factors – age, angular position, extent of eruption, and/or the interaction
between the factors – had a significant influence on the assessment on the indications for removal of molars without disease, it was tested using three-way ANOVA. The level of significance was set at P=0.05. The coefficient of determination (R2) indicated the extent to which the variation in the assessment of the indication for removal was explained by the three factors and their interactions in molars without disease. Overall the level of significance was set at P=0.05.
RESULTS Patients, and clinical state of molars The results were based on the data from 666 mandibular third molars (one molar per patient). The mean age of the patients was 29 years (range 15–80). Four hundred and seventy one (71%) of the patients were aged between 15 and 29 years. Three hundred and fifty (53%) of the patients were female. One hundred and eighteen molars (18%) showed no disease and 548 molars (82%) did. In 465 molars one disease was recorded, in 77 two, and in six molars three (Table 1). In patients aged 50 or more, all third molars were associated with some disease. Three hundred and ninety nine (60%) of the removed molars were partially covered by soft tissue, 154 (23%) were completely covered by soft tissue, only 32 (5%) were completely covered by bone tissue and 81 (12%) were fully erupted, i.e. not impacted. About one-third of all molars removed, 221, were in a mesioangular position, followed by vertical 191 (29%), distoangular 139 (21%) and horizontal 115 (17%).
Oral surgeons’ assessment of the indications for removal expressed in the VAS The assessment of the indication varied substantially – between 0 and 100 – for molars without disease (Table 1). The SD was higher for this group of molars compared with those with some associated disease. The mean VAS for removal of molars without disease was significantly lower than that for molars with associated disease (Table 2). The differences between the mean VAS for molars with one compared with two or three diseases were not significant. Table 3 shows the number of molars without disease and the mean and median VAS according to:
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British Journal of Oral and Maxillofacial Surgery
Table 3 – Mandibular third molars that were removed prophylactically. Number of removed molars (n=118) in patients of different agegroups and molars of different angular positions and extent of eruption, and oral surgeons’ assessment of the indication for removal expressed as mean and median indication on VAS (0= weak and 100= strong indication for removal) No. of molars
VAS (mm) Mean (SD)
VAS (mm) Median (Range)
36 70 10 2
47 (27) 43 (26) 27 (18) 92 (11)
50 (3–91) 38 (0–98) 24 (2–58) 92 (84–100)
21 60 7 30
46 (26) 44 (28) 45 (33) 43 (26)
46 (10–98) 37.5 (0–100) 27 (7–93) 36.5 (4–95)
6 45
40 (27) 45 (26)
36.5 (11–80) 46 (7–98)
49
44 (24)
38 (0–95)
18
42 (36)
30 (0–100)
Age-group (years) 15–19 20–29 30–39 40–49 Angular position Vertical Mesioangular Distoangular Horizontal Extent of eruption Fully erupted Partially covered by soft tissue Completely covered by soft tissue Completely covered by bone tissue
patients’ age-group; angular positions; and extent of eruption of the molars. Considering age-group, the highest mean and median VAS were given for two patients in the age-group 40–49; both the molars were removed before orthognathic surgery. The mean VAS were comparable for different angular positions and different extent of eruption, but presented a slightly higher variation in median VAS. Excluding the two oldest patients, the patients’ age was the only factor that had a significant effect on the assessment of the indication (P< 0.05) for molars without disease, so the indication was highest for patients of the youngest agegroup and lowest for patients of the oldest age-group. The coefficient of determination (R2) was 0.20 for molars without disease, i.e. the mean proportion of the variation explained by the three factors and the interaction between the factors that influenced the surgeons’ assessment of the indication for removal was 20%.
DISCUSSION In decision-making, we judge whether to act or not – in this case, whether to remove or not to remove a mandibular third molar. Even when we choose an action, there will be the question of how certain we are that the action was correct. In addition to the VAS as used in the present study, receiver operating characteristics (ROC) analysis has been used to study practitioners’ certainty in decision making about third molar removal.13 The results of studies of decision making in endodontics have shown that clinicians do not approach evaluation of treatment as clear-cut but rather operate along a continuum.14 Although the oral surgeons removed all the molars, they gave molars without disease significantly weaker
mean indications than molars with disease. In one sense, this might reflect the surgeons’ doubts about the prophylactic removal of mandibular third molars. Assessments of the indications for removal of molars without disease covered a wide range, between 0 and 100, probably related to the surgeons’ predicted risk of the development of a disease. This is supported by the results of a previous study on dentists’ judgements about the removal of asymptomatic mandibular third molars.15 This study showed that there was a good correlation between each dentist’s indications for removal of a molar and the predicted risk of the development of disease. This judgemental behaviour – the process of inference that precedes a decision – as assessed with the VAS, might indicate the oral surgeons’ limited knowledge about whether or not the third molars would develop disease. This variation in judgemental behaviour can be expected as the natural history of the mandibular third molar is unknown and reported evidence about which molars will develop disease. Of the three factors analysed, the patient’s age was the only one that influenced the oral surgeons’ assessment of the indications in molars without disease. The oral surgeons did not discriminate between molars in different eruptive states or angular positions. Reported evidence3 shows that molars that are partly covered by soft tissue have a 22–34 times higher risk of developing disease than those at other stages of eruption. Molars that are completely covered by soft tissue and molars covered by bone tissue have about an equal risk of developing a disease.3 Distoangular molars have a 5–12 times higher risk of developing a disease than those in other angular positions.3 Despite this evidence, the coefficient of determination for molars without disease was rather low (0.20), and was explained by the three factors – patient’s age, and
Mandibular third molars: indications for removal
angular and eruptive position of the molar. In addition to the patient’s age, other factors such as oral hygiene, and the patient’s degree of caries and periodontitis may have influenced the oral surgeon’s judgement. Another explanation for the low values of R2 might be a lack of cognitive control16 – that means that the oral surgeons were not able to make judgements according to their policy. They might have had problems translating the complexity of the judgement into an assessment on the VAS. The results of this study indicate that there was an awareness among the oral surgeons that prophylactic removal of mandibular third molars could be questioned. When clinicians make their judgements and decisions about treatment they have to deal with the uncertainty and uniqueness of each individual patient.15 We think that greater attention should be paid to the knowledge on which one’s judgements are based. With this study, we hope to increase oral surgeons’ interest in the judgements and decisions that precede the treatment of third molars. Acknowledgement This project was supported by grants from the Swedish Medical Research Council (grant 11647) and the Faculty of Odontology, Malmö University, Sweden.
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7. Eddy DM. Medical decision making: from theory to practice. Anatomy of decision. J Am Dent Assoc 1990; 263: 441–443. 8. Knutsson K, Brehmer B, Lysell L, Rohlin M. General dental practitioners’ evaluation of the need for extraction of asymptomatic mandibular third molars. Community Dent Oral Epidemiol 1992; 20: 347–350. 9. Knutsson K, Brehmer B, Lysell L, Rohlin M. Asymptomatic mandibular third molars: oral surgeons’ judgement of the need for extraction. J Oral Maxillofac Surg 1992; 50: 329–333. 10. Baron J. What is thinking? In: Baron J, ed. Thinking and deciding, 2nd edn. Cambridge: Cambridge University Press, 1994; 3–15. 11. Lysell L, Brehmer B, Knutsson K, Rohlin M. Rating the preventive indication for mandibular third molar surgery. The appropriateness of the visual analogue scale. Acta Odontol Scand 1995; 53: 60–64. 12. Winter GB, ed. Principles of Exodontia as Applied to the Impacted Third Molar. St Louis: American Medical Books, 1926. 13. Brickley M, Kay E, Shephard JP. Public health aspects of third molar surgery. The effect of surgeons’ treatment thresholds on efficiency and effectiveness. Community Dent Health 1995; 12: 70–76. 14. Kvist T, Reit C, Esposito M et al. Prescribing endodontic retreatment: towards a theory of dentist behaviour. Int Endod J 1994; 27: 285–290. 15. Knutsson K, Brehmer B, Lysell L, Rohlin M. Mandibular third molar as mediated by three cues. Dentists’ treatment decisions on asymptomatic molars compared with molars associated with pathologic conditions. Acta Odontol Scand 1997; 55: 372–377. 16. Brehmer A, Brehmer B. What have we learned about human judgement from thirty years of policy capturing? In: Brehmer B, Joyce CRB, ed. Human judgement. The SJT view. Amsterdam: Elsevier, 1988: 75–114.
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The Authors R. Liedholm DDS Lecturer, Department of Oral Surgery K. Knutsson DDS, Odont Dr Research Associate, Department of Oral Radiology M. Rohlin DDS, Odont Dr Professor, Head, Department of Oral Radiology, Faculty of Odontology, Malmö University, Malmö, Sweden L. Lysell DDS, Odont Dr Head, Department of Oral Surgery, Central Hospital, Kristianstad, Sweden Correspondence and requests for offprints to: Dr Rolf Liedholm, Department of Oral Surgery, Faculty of Odontology, Malmö University, 214 21 Malmö, Sweden. Tel: + 46 40 322000; Fax: + 46 40 322046 Paper received 9 February 1998 Accepted 17 March 1998