British Journal of Orthodontics

ISSN: 0301-228X (Print) (Online) Journal homepage:

The Mandibular Third Molar and Late Crowding of the Mandibular Incisors—A Review N. S. Vasir B.D.S., M.Sc., M.Orth., F.D.S. & R. J. Robinson B.D.S., M.Sc., D.Orth., F.D.S. To cite this article: N. S. Vasir B.D.S., M.Sc., M.Orth., F.D.S. & R. J. Robinson B.D.S., M.Sc., D.Orth., F.D.S. (1991) The Mandibular Third Molar and Late Crowding of the Mandibular Incisors—A Review, British Journal of Orthodontics, 18:1, 59-66, DOI: 10.1179/bjo.18.1.59 To link to this article:

Published online: 21 Jun 2016.

Submit your article to this journal

View related articles

Citing articles: 19 View citing articles

Full Terms & Conditions of access and use can be found at Download by: [Tufts University]

Date: 06 March 2017, At: 16:51

British Journal of Orthodontics/Vol. 18/1991/59-66

Review Article The Mandibular Third Molar and Late Crowding of the Mandibular IncisorsA Review N. S. VASIR, B.D.S., M.Sc., M.ORTH., F.D.S. Orthodontic Department, University College, and Middlesex School of Dentistry, Mortimer Market, London WCIE 6lD R. J. RoBJNSON, B.D.S., M.Sc., D.ORTH., F.D.S. Torbay Hospital, Lawes Bridge, Torquay TQ2 7AA Received for publication November 1989

Abstract. The role of the mandibular third molar in late incisor crowding remains controversial. Detailed examination of frequently quoted.studies indicates a small, but statistically significant relationship. The clinical relevance of this is discussed. Index words: Third Molars, Lower Incisor Crowding.


Late crowding of the mandibular dentition is very common and usually manifests itself in the incisor region (Sakuda et al., 1976). It is often presumed that this crowding of the mandibular incisors is associated with the presence of erupted third molars. A survey of a large number of orthodontists and oral surgeons showed that 65 per cent of both groups believed in a cause-effect relationship (Laskin, 1971 ). Lysell and Rohlin ( 1988) reported that between the ages of l 0-19 years, more than 50 per cent of third molars were removed for orthodontic considerations. Debate over this issue has raged for more than a century. Robinson, in 1859, incriminated the third molar in the aetiology of this crowding. However, the predominant view is that the crowding seen with the erupting or erupted third molars has a multifactorial aetiology. Nine factors are most frequently quoted. I. Anterior growth and remodelling of the mandible

Mandibular incisor crowding may be caused by the continued growth of the mandible after maxillary 030 I-228X(91/004000 + 00102.00

growth has ceased, leading to restriction of the lower arch by the upper arch (Broadbent, 1943; Bjork and Palling, 1955; Moore, 1960)_

2. Pre-existing tooth-tissue discrepancy Richardson (1982) reported that patients with crowding of the early permanent dentition are more likely to result in impaction of the third molars. Robinson (1981) demonstrated an association, albeit small, between the degree of lower labial segment crowding in the early permanent dentition and the degree of crowding in late adolescence, in a group of treated patients. 3. Mesial drift

Mesial migration of posterior teeth may contribute to anterior crowding. Studies on monkeys in which the gingival tissues were removed unilaterally showed that the trans-septal fibres were important in this phenomenon (Moss and Picton, 1972). This movement may, in part, be dependent on growth changes in the lower face (Stephens and Houston, 1984). rt• 1991 British Society for the Study of Orthodontics

60 N. S. Vasir and R. J. Robinson

4. Anterior component offorce of the occlusion Van Beek and Fidler ( 1977) and van Beek ( 1979) demonstrated that occlusion was a significant factor in anterior movement of the dentition and claimed that this was more important than the effect of the transseptal fibres. Moss and Picton ( 1967) were unable to confirm that occlusion contributed to mesial drift. 5. Soft tissue maturation

Van der Linden ( 1979) stated that changes in tone and elasticity of the facial mask may affect the position of the teeth. Richardson ( 1980) questioned the effect of increased pressure acting on the lower labial segment without affecting the upper incisors. 6. Tooth size and shape Crowding has been associated with large teeth (Norderval et al., 1975). Peck and Peck ( 1972, 1975) found that crown shape was a determining factor in mandibular crowding. They advocated removal of interproximal enamel to correct the ratio of the facio-lingual dimension and the mesiodistal width of the lower incisors, to a value calculated from a group of non-crowded patients.

7. Lack of attrition Begg ( 1954) examined aboriginal dentitions which showed extensive attrition. He concluded that a change to a less fibrous diet in modern man had resulted in less attrition and, therefore, more dental crowding. 8. Difference between the evolutionary reduction of tooth size and jaw size Many studies have shown there to be an evolutionary reduction of tooth size which is slower than reduction of jaw size (Smyth, 1933; Bjork, 1950; Fishman, 1976). This difference may first appear as late incisor crowding in many patients. 9. The mandibular third molar The third molar exhibits the greatest variation of any tooth in the human dentition. Developmental absence arises in 13-15 per cent of patients, making these teeth the most commonly missing of the permanent series (Grahnen, 1956; Davies, 1968). The incidence of impaction of lower third molars ranges from 9 to 24 per cent (Hellman, 1936; Bjork et al., 1956; Dachi and Howell, 1961; Morris and Jerman. 1971).

BJO Vol. IX No. I

This review of the relevant literature is not exhaustive. Many of those studies mentioned are often quoted in the literature, but close appraisal of the evidence on which the conclusions were based can show deficiencies. Most of the studies examined were cross-sectional and broadly similar in that they compared groups in which the third molars were present with groups where they were absent. Bergstrom and Jensen ( 1960) examined a sample of 30 individuals with unilateral aplasia of the mandibular third molars. The crowding on the side with the third molar was found to be, on average, 0·64 mm greater than that found on the side where the third molar was absent. The average mesial movement of the second molar was greater on the side with the third molar present. The centre line was displaced to the side without the third molar, although the degree of displacement was not statistically significant. The above changes implied an association between lower incisor crowding and presence of the third molar. The paper showed some shortcomings. I Determination of method error: this was not fully explained and it was unclear if it was related to the crowding on each side or the difference in crowding between the two sides. It is important to ascertain if the variability due to measurement is a large proportion of the actual difference between the two sides as this may reduce the true statistical significance of a small real difference between the two sides. 2 Data presentation: the paper quoted standard error of the mean (value± 0·23 mm) instead of standard deviation in relation to the small (0·64 mm) difference between the sides in the mandibular arch. Assuming a normal distribution, the recalculated value for standard deviation (SD = 1·23 mm) implies that there were some patients in whom the crowding was worse on the side with the third molar missing. 3 Methodology: the authors stated that well aligned arches were not measured. This introduced an element of bias in the assessment of crowding and then the statistics could not truly reflect the sample. The conclusion of this paper was that it indicated a relationship between the third molars and crowding in the mandibular arch, but the data presentation clouded the significance of the small real difference between the sides. A cross-sectional study by Shanley ( 1962) is often quoted as evidence against an association between mandibular third molar and late crowding. Unfor-

BJO f£·bruury lW/

tunately, the lack of detail given in this study, which was published in abstract form, makes it difficult to evaluate. The small numbers in each group (44 patients in total) means that very large differences between groups would be necessary to show statistically significant changes. Vego (1962) studied the change in mandibular arch length in two untreated groups. One group consisted of 40 patients with lower third molars present and the other group consisted of 25 patients with these teeth absent. Measurements were made soon after eruption of the second molar and again at an age greater than 17 years. He found that the group with the third molars p~esent had a mean increase in crowding of 2·5 mm compared to 1·7 mm in the group with third molars absent. The difference between the two groups (0·8 mm) was statistically significant. Although this study indicated that the presence of the third molar is associated with an increase in crowding of the lower arch, Vego did not report the error of the measurement. Instead, he quoted his statistician who stated that this was superfluous as only differences were being examined! Vego found a smaller mean loss in arch length in the group with absent third molars. Garn and Lewis (1962) found an association between missing teeth and reduction in size of remaining teeth. Similar findings were reported by Lavelle et al. ( 1970). This may be a more significant factor than the presence or absence of the third molar per se in explaining the difference between the two groups. Keene (1964) published a study which investigated the relationship between third molar agenesis, spacing, and crowding of the teeth and tooth size in caries resistant naval recruits. He studied the distribution of patients with crowding in each of the three groups. In the group with all four third molars present, 48 per cent were assessed to have mandibular crowding. In the patients with one or more third molars absent, 30 per cent were found to have mandibular crowding. When the patients with all four third molars absent were looked at separately, only 25 per cent presented with mandibular crowding. This would indicate that the absence of third molars is associated with a smaller degree of crowding. The author also found that the mesiodistal width of the lower right first molar was smaller in the agenesis group, lending evidence to the contention that missing teeth are associated with smaller teeth. This, in itself, may result in the smaller incidence of crowding in patients with third molar agenesis. The method used to assess crowding was somewhat empirical. Spacing was assessed as 'the regular arrangement of teeth with one or more spaces

Late Crowding 61

present', crowding as 'the irregular arrangement of teeth evidenced by overlapping of proximal surfaces or buccolingual displacement of one or more teeth'. Although the paper showed an association between missing teeth and reduction in size of remaining teeth, it did not positively incriminate third molars as contributing to crowding. Schwarze (1973) published data of 100 patients who had third molars germectomized at ages ranging from 12 to 22 years. There were 49 controls 'comparable in age and anomalies'. Using a photodocumentation method (Schwarze, 1972), he demonstrated that the lower first molar in the control group was carried forward by an average of I· 5 mm more than in the germectomy group. The author was very positive in proclaiming the obvious nature of this change, inferring that the third molars influenced mesial movement of the dentition. This study can be criticized from a number of aspects; all the patients underwent active orthodontic treatment which may have affected the eventual alignment and position of teeth used to indicate a difference in this study. Also, no additional teeth were extracted apart from the third molars in the germectomy group. This may have a significant bearing on the outcome especially as patients were selected to undergo germectomy of their third molars if they presented with a 'strong tendency to crowding and relapse'. What is described as the 'wisdom tooth' factor in causing the relatively more mesial movement of the first molar could easily be the strong tendency to crowding in the germectomy group dissipating distally and, thus, countering the mesial movement of the first molars. Richardson ( 1989d, b), in an analysis of longitudinal data on third molar development indicates that there is less forward movement of the first molar in the presence of severe anterior crowding. Furthermore, the influence of the mandibular third molars was found to be most pronounced at the age of about 16 years which would appear to be slightly early in relation to the late crowding of the incisors. The error of the method was quoted as being within I per cent. This seems low and there is no description of the actual method of error assessment. This study only measured mesial movement of the first molar and assumed that this would be transferred to the lower incisors. This assumption is not entirely justified, although it is rare to see late crowding confined to the premolar region. Kaplan (1974) published an investigation of the post-treatment changes in 75 patients treated with fixed appliances. Thirty presented with erupted lower third molars, 20 with these teeth impacted and in 25 patients they were absent. Some patients were treated with extractions (n=47) and some

62 N. S. Vasir and R. J. Robinson

BJO Vol. 18 No. I

non-extraction (n = 28). An analysis of variance changes in the same direction indicating that the revealed no significant differences between the presence of third molars and perhaps more imporgroups. He therefore concluded that the third molar tantly the eruption of these teeth, contributed to a was not related to late crowding of lower incisors. mesial movement of the dentition with a concomiOn close examination of the published data, a tant increase in lower incisor crowding. This condifferent interpretation can be placed on the figures, trasts markedly with Kaplan's conclusions and if subjected to a Students t test. However, the supports the role of third molars in the late 'disparity between the numbers in each group and crowding of lower incisors. between the variances of some of the samples, Lindquist and Thilander ( 1981) published the suggests that non-parametric tests would be more results of an elaborate study carried out on 52 suitable. Without access to the raw data, it is children, to ascertain whether the mandibular third impossible to determine if the data was normally molar in combination with other variables contridistributed or if non-parametric tests would be buted to late incisor crowding. Patients with both more appropriate. If the t test is applied to the data mandibular third molars present were selected. A available, different conclusions can be reached- randomly selected third molar was surgically crowding was measured by Little's method (1975) removed from each patient. The non-extraction side as the sum of the displacements of the contact was used as a control. The results of the cephalopoints of the lower incisors. The cohort of patients metric analysis did not yield any positive findings, treated by extractions, showed an average increase leading the authors to conclude that 'lower arch in anterior crowding of 1·5 mm greater in the group crowding is obviously too complex to allow the with the third molars erupted when compared to the cephalometric system used to discriminate small group where these teeth were absent. When extrac- changes in lower arch length'. However, cast analytion and non-extraction groups were combined, sis indicated that space conditions improved on the there remained a statistically significant difference, extraction side in 70 per cent of the patients, but albeit small, of I mm. This lends evidence to the worsened in the remaining 30 per cent. Extraction opinion that erupted third molars are associated of the mandibular third molar was found to be beneficial in patients with severe initial crowding. with late crowding of lower incisors. The assessment of results in this paper is difficult The change in axial inclination of lower incisors to the mandibular plane was 2·5 degrees more in the due to poor presentation of data. The 'regression group with third molars erupted when compared line method' which is the basis for interpretation of with the agenesis group. The difference was even the results of the cast analysis, is not discussed nor is greater between the impacted and absent groups. there any description of the 'modified Schwartz This suggested that the presence of third molars method' for orientation of the casts. The latter technique involves the midline from the maxillary may contribute to proclination of lower incisors. Horizontal movement of the lower incisor tip was incisors being transferred to the lower arch for measured by superimposing tracings of post-treat- assessment of changes in the lower centre line. The ment and post-retention radiographs using the main positive conclusions of this paper are based on mandibular stable structures as described by Bjork a difference between the arch length on the control (1969) and projecting the incisal tip onto a con- and experimental side, using the transferred referstructed horizontal co-ordinate. The lower incisor ence line. The quoted mean difference is 0·16 mm (range tip moved 1 mm further anteriorly in the group with third molars erupted when compared with the +0·8 to -0·4 mm) without any documentation of group with these teeth absent. A similar change was the error of the method: This study had many found in the mesial movement of a point projected shortcomings eluded to earlier in the review of the onto the same co-ordinate from· the first molar. paper by Bergstrom and Jensen ( 1960). In 1982, Richard son published a paper using data These changes reflected a greater reduction in arch length. When drawing conclusions from Kaplan's gathered from a longitudinal study of third molar data, it must be borne in mind that Little's method eruption. Records were obtained upon establishis merely an irregularity index. Contact points may ment of the permanent dentition (approximately 13 also be displaced in non-crowded and spaced years of age) and repeated 5 years later. Part of the arches. Also, there was confusion over the terms sample was divided into two groups, one with post-treatment and post-retention. If measure- bilateral impaction of third molars and the other ments were made on models immediately following without impactions. Richardson found a millimetre removal of bands, changes in alignment could occur more original anterior crowding in the impacted through settling of the occlusion utilizing band group. There was no difference in the changes of spaces. The factors discussed above showed crowding over the period of observation; crowding

BJO February 1991

increased by approximately 2 mm in each group. She concluded that 'original molar crowding and later decrease in that crowding are both associated to some extent with the development oflate anterior crowding'. This suggested that there was transference of crowding from the molar region to the front of the arch. Richardson also concluded that 'individuals whose lower third molars later become impacted tend to have more crowding of the early permanent dentition, both anteriorly and in the molar region, than those whose third molars erupt normally'. This implied that third molar impaction is a manifestation of overall crowding of the dentition. It was also foupd that the impacted group had larger teeth on average which would increase the tooth-tissue ratio. Measurements were made to within 0·5 mm, but the method of error determination was not reported. There is also uncertainty as to whether or not extractions were performed as part of earlier orthodontic treatment in either arch. Although this paper showed an association between early crowding and late crowding, it shed little light on the role of the third molar in late crowding of the lower incisors.

Discussion The variance in conclusion reached by the studies on mandibular third molars and late crowding of lower incisors would indicate that clear clinical guide-lines cannot, as yet be adopted. The controversy shall continue whilst clinical hunches prevail in the absence of clear evidence and misinterpretation of studies adds to the confusion. Bjork and Skieller ( 1972), for example, did not specifically examine the role of third molars in crowding. Patients in their samples had not completed jaw growth as the study was confined to a period 6 years around puberty. Their finding that shortening of the dental arches manifesting itself before roots of the third molar had appreciably developed is not totally relevant to the issue of secondary crowding and third molars. Both Graber and Kaineg (1981 ), and Lindquist and Thilander (1982) quote the same study as providing no clear evidence that secondary crowding could be assigned to third molars. It is incumbent on reviewers to read articles fully and context correctly. Similarly, a limited perspective on the issue supporting for example, 'the pressure from back of the arch' hypothesis (Richardson, 1989a, b) is likely to elicit an emotional rather than constructive response (Reidel, 1989). However, use of data from an 'intact' mandibular arch of a patient receiving treatment, with or without extractions, in the maxillary arch cannot be regarded as valid for a

Late Crowding 63

study of causative factors in relation to lower incisor crowding. Much of the evidence incriminating the third molar is from material where this tooth is developmentally absent in one quadrant. The association between hypodontia and microdontia (Baum and Cohen, 1971; Garn et al., 1963; Garn and Lewis, 1970) would mean that there would be less crowding in patients with absence of the third molar. However, other studies did not support this finding (Christensen and Melsen, 1974). Similar difficulties are encountered when comparing one side of the mandibular arch where the third molar is either extracted or missing with the contralateral side. Generally, the differences are small and use of the midline which is a common point, could obscure or exaggerate a real difference (Houston, 1983). Isolated case reports (Stephens, 1980) cannot justifiably be used as supporting evidence in this issue.

Conclusions If interpretation of data from the studies reviewed is accepted, then the conclusions would be that the mandibular third molar has a statistically weak association with late crowding of lower incisors. The process of eruption of third molar may be implicated in the mechanism of this crowding. It is plausible that, in specific cases, the mandibular third molar may contribute towards deterioration of incisor alignment. However, because of the wide variation in all the factors examined thus far and the small differences detected, the identification of such patients and the assessment of the relative contribution of the third molar is likely to elude future studies. The role of the mandibular third molar in late incisor crowding takes undue prominence in the literature. This partly fulfils an orthodontic need to find a satisfactory explanation for this change in late adolescence. The coincidence of both events' in terms of development cannot be ruled out. In addition, the potential for further reduction in mandibular anterior dimensions continues well beyond the second decade (Smith and Bailit, 1977). Helm and Petersen (1989), in a longitudinal study from adolescence to 35 years of age, found that the most conspicuous change observed was an increase in the frequency of mandibular crowding, predominantly in the incisor region. They also demonstrated a reduction in the vertical dimension over this period. Perhaps the morphology of the incisors, their vertical relationship, mandibular form and function, and soft tissue patterns are amongst factors that require further investigation. Ideally, randomized control trials

64 N. S. Vasir and R. J. Robinson

with large samples, matched in respect of specific variables, will provide clear answers. Clinical implications

Despite considerable research on this subject, the type of patient in whom removal of third molars would have a beneficial effect on mandibular incisor alignment is difficult to identify. Even where there is an effect, it is likely to be minimal. The decision to extract mandibular third molars in order to prevent or minimize deterioration of incisor alignment should not be made without careful evaluation of its potential usefulness or handicap to the dental health of the individual-the mandibular third molar, situated at the end of the dental arch is frequently affected by space deficiencies. Its impaction can cause an array of painful problems of sufficient gravity to justify its removal. Perhaps of a more insidious nature are functional problems due to a partially erupted third molar and an overerupted antagonist, resulting in occlusal derangements. With all of these potential problems, one might be tempted to advise early removal of the mandibular third molar in the young adult concerned about the malalignment of the mandibular incisors. This view must be balanced against the knowledge that its removal is not risk free. Moreover, a third molar may substitute very effectively for another tooth in the same quadrant. Thoughtless removal can condemn a patient to unnecessary occlusal handicap and possibly extensive restorative treatment. The options are· clearer in patients requiring active orthodontic treatment. Crowding is the most common feature requiring correction. Dierkes ( 1975) found that removal of the first or second premolar provided more space for eruption of third molars when compared to patients treated nonextraction. Richardson (l989a, b), in comparing 48 first premolar extraction cases with 46 non-extraction cases found a greater increase in molar space in the extraction cases, suggesting that this would account for the reduced incidence of third molar impaction found in earlier studies (Faubian, 1969; Richardson. 1976). Extraction of the second, rather than the first premolar appears to be more favourable for third molar eruption (Perlow, 1964), but not necessarily for its final position. Plint ( 1970) studied records of 75 patients and concluded that loss of first permanent molars provided available space in the dental arches for the majority of third molar teeth. Richardson (1975) found that mandibular third molar extraction was virtually eliminated following extraction of a first or second molar. The question of whether to remove third molars

BJO Vol. 18 No. I

early when other extractions for orthodontic reasons are either not required or the crowding is acceptable to the patient remains unanswered. Interpretation of the data from studies presently available indicates that the mandibular third molar has a small, but variable effect on lower incisor crowding. The prediction of third molar behaviour under these circumstances requires a separate review.


We are indebted to Mr D. A. Plint for his support and advice.

References Baum, B. J. and Cohen, M. M. (1971) Agenesis and tooth size in the permanent dentition, The Angle Orthodontist, 41, 100- 102.

8ega, P. R. (1954) Stone age man's dentition, American Journal of Orthodontics, 40, 298-312. Bergstrom, K. and Jensen, R. (1960) The significance of the third molars in the aetiology of crowding. A biometric study of unilateral aplasia of the third molars, Transaelions of the European Orthodontic Society, 84-96. Bjork, A. (1950) Some biological aspects of prognathism and occlusion of the teeth, Acta Odonwlogica Scandinat•im, 8, I 40. Bjork, A. (1969) Prediction of mandibular growth rotation, American Journal of Orthodontics, 55, 585 599. Bjork, A. and Palling, M. (1955) Adolescent age changes in sagittal jaw relations, alveolar prognathy, and mesial inclination, Acta Odomologica Scandinavica, 12, 201 232. Bjork, A. and Skieller, V. (1972) Facial development and tooth eruption. An implant study at the age of puberty, American Journal of Orthodontics, 62, 339-383. Bjork, A., Jensen, E. and Palling, M. (1966) Mandibular growth and third molar impaction, Acta Odontologica Scandinm•ica, 14, 231-272. Broadbent, B. H. (1943) The influence of the third molars on the alignment of the teeth, American Journal of OrthodontiC.\' & Oral Surgery, 29, 312-330. Chrlstlansen, H. C. and Melsen, B. (1974) Relationship between tooth size and third molar agenesis, Scandinavian Journal of Denial Research, 82, 552-556. Oachl, S. F. and Howell, F. V. (1961) A survey of 3874 routine full mouth radiographs. 11. A study of impacted teeth, Oral Surgery, 14, 11651169. Davles, P. L. (1968) Agenesis of teeth of the permanent dentition. A frequency study of Sydney schoolchildren, Australian Dental Journal, 13, 146-150.

BJO fi·hruary 1991

Late Crowding 65

Dierkes, D. D. (1975) An investigation of the mandibular third molar in orthodontic cases, The Angle Orilwdonlisl, 45, 207 212.

Lysell, L. and Rohlin, M. (1988) A study of indications used for removal of the mandibular third molar, International Journal of Oral M axillt!/{u·ial Surgny, 17, 161-164.

Faubian, B. H. (1969) Effect of extraction of premolars on eruption of mandibular third molars, Journal of' Amerimn Dt•lllal As.mciaJion, 76, 316 320.

Moore, A. N. (1960) Inadequacy of mandibular anchorage, American Journal t~l Ortlwdolllics, 46, 440 454.

Fishman, L. S. (1976) Dental and skeletal relationships to attritional occlusion, The Angle Orilwdontist, 46, 51 63. Garn, S. M. and Lewis, A. B. (1962) The relationship between third molar agenesis and reduction in tooth number, The Angle Orthodontist, 32, 14 18. Garn, S. M. and Lewis, A. B. (1970) Effect of agenesis on the crown-size profile pattern, Journal of' Dental Rt•search, 48, 1314. Garn, S. M., Lewis, A. B. and Kerewsky, R. S. (1963) Third molm agenesis and size reduction of the remaining teeth, Nature, 200, 488 -489. Graber, T. and Kaineg, T. E. (1981) The mandibular third molar-its predictive status and role in lower incisor crowding, Proceedings of' the Finnish Dental Society, 77, 37 44. Grahnen, H. (1956) Hypodontia in the permanent dentition, Odontologica Rer•y, 7, I 100.

Morris, C. R. and Jerman, A. C. (1971) Panoramic radiographic survey: a study of embedded third molars, Journal t~l Oral Surgery, 29, 122-125. Moss, J. P. and Picton, D. A. (1967) Experimental mesial drift in adult monkeys (Macaca irus), Archir•es (){Oral Biology, 12, 1313 · 1320. Moss, J. P. and Picton, D. A. (1972) The migration of teeth in adult monkeys, Transactions ~~l the European Orthodontic Society, 443-451. Norderval, K., Wlsth, P. J. and Boe, 0. E. (1975) Mandibular anterior crowding in relation to tooth size and craniofacial morphology, Scandinaz•ian Journal()( Dell/a/ Research, 83, 267-273. Peck, H. and Peck, S. (1972) An index for assessing tooth shape deviations as applied to the mandibular incisors, American Journal()/' Orthodontics, 61, 148-153. Peck, H. and Peck, S. (1975) Orthodontic aspects of dental anthropology. The Angle Orthodontist. 45, 95 102.

Hellman, M. (1936) Our third molar teeth: their eruption, presence and absence, Dental Cosmos, 78, 750-762.

Perlow, J. A. (1964) A full light-arch technique utilising Dull's principles of extraction treatment with emphasis on twenty-eight teeth, American Journal of Orthodontics, SO, 81 98.

Helm, S. and Petersen, P. E. (1989) Individual changes in malocclusion from adolescence to 35 years of age, Acta Odontologica Scandinal'ica, 47, 193-252.

Plint, D. A. (1970) The effect on the occlusion of the loss of one or more first permanent molars, Transactions of the European Orthodontic Society, 329-336.

Houston, W. J. B. (1983) The analysis of errors in orthodontic measurements, American Journal(){ Orthodontics, 83, 382-390.

Reidel, R. A. (1989) Role of the mandibular third molar relative to lower arch crowding: letter to the editor, American Journal(){ Orthodolllics, 95, 25A.

Kaplan, R. G. (1974) Mandibular third molars and postretention crowding, American Journal of Ortlwdontics, 66, 411-430. Keene, H. J. (1964) Third molar agenesis, spacing and crowding of teeth, and tooth size in caries-resistant naval recruits, American Journal of Orthodolllics, SO, 445-451. Laskin, D. M. (1971) Evaluation of the Third Molar Problem, Journal (){American Dental Association, 82, 824-828. Lavelle, C. L. B., Ashton, E. J. and Flinn, R. M. (1970) Cusp pattern, tooth size and third molar agenesis in the human mandibular dentition, Archir•es of Oral Biology, IS, 227-237. Lindqvist, B. and Thilander, B. (1982) Extraction of third molars in cases of anticipated crowding in the lower jaw, American Journal of Ortlwdontics, 81, 130· I 39. Little, R. M. (1975) The Irregularity Index: a quantitative score of mandibular anterior alignment, American Journal of' Ortlwdontics, 68, 554-563.

Richardson, M. E. (1975) The relative effects of the extraction of various teeth on the development of mandibular third molars, Transactions of the European Orthodontic Society, 79-85. Richardson, M. E. (1980) The aetiology of lower arch crowding, Journal of the Irish Demal Association, 26, 26-31. Richardson, M. E. (1982) Late lower arch crowding in relation to primary crowding, The Angle Orthodontist, 52, 301 312. Richardson, M. E. (1989a) Role of the third molar in the cause of late lower arch crowding: a review, American Journal ofOrtlwdontics, 95, 79-83. Rlchardson, M. E. (1989b) The effect of mandibular first premolar extraction on third molar space, The Angle Orthodontist, 59, 291-294. Robinson, J. (1859) The causes of irregularities of the teeth. Dental review, In: Weinberger B. W. ( 1926) Orthodolllics: An historical review of its origin and evolution, Vol. I. C. V. Mosby Company, 325.

66 N. S. Vasir and R. J. Robinson Robinson, R. J. (1981) An investigation into the behaviour of cranio-facial variables and their relationship to late lower incisor crowding in a group of treated cases, MSc Dissertation, University of London. Sakuda, M., Kuroda, Y., Wada, K. and Matsumoto, M. (1976) Changes in crowding of teeth during adolescence and their relationship to the growth of the facial skeleton, Transactions of the European Orthodontic Society, 93-104.

BJO Vol. 18 No. I

Stephens, C. D. (1980) The effect of third molar removal on the size of premolar extraction spaces in the lower arch, British Journal of Orthodontics, 7, 189-193. Stephens, C. D. and Houston, W. J. B. (1984) Facial growth and lower premolar extraction space closure, European Journal tJ{Ortlwdolllics, 7, 157-162.

Schwarze, C. W. (1972) Expansion and relapse in long follow-up studies, Transactions C!fthe European Orthodontic Society, 263-272.

van Reek, H. (1979) The transfer of mesial drift potential along the dental arch in Macaca irus: an experimental study of tooth migration rate related to the horizontal vectors of occlusal forces, European Journal C!{ Orthodontics, I, 125-129.

Schwarze, C. W. (1973) The influence of third molar germectomia-A comparative longterm study, Ab.1·trt1ct of Third International Congress. London, 551-562.

van Reek, H. and Fidler, V. J. (1977) An experimental study of the effect of functional occlusion on mesial tooth migration in macaca monkeys, Archives of Oral Biology, 22, 269-271.

Shanley, L. S. (1962) Influence of mandibular third molars on mandibular anterior teeth, American Journal of Orthodontics, 48, 786.

Van der Linden, F. P. G. M. (1979) Changes in the dentofacial complex during and after orthodontic treatment, European Journal of Orthodontics, I, 97-105. Vego, L. (1962) A longitudinal study of mandibular arch perimeter, The Angle Orthodontist, 32, 187 192.

Smith, R. J. and Balllt, H. L. (1977) Variation in dental occlusion and arches among Melanesians of Bougainville Island, Papua New Guinea, American Journal of Physical Anthropology, 47, 195~-208. Smyth, C. (1933) Facial growth in children with special reference to the dentition, H.M.S.O., London.

The mandibular third molar and late crowding of the mandibular incisors--a review.

The role of the mandibular third molar in late incisor crowding remains controversial. Detailed examination of frequently quoted studies indicates a s...
886KB Sizes 0 Downloads 0 Views