Ades AG, Joondeph DR, Little RM, Chapko MK.
A long-term study of the relationship of third molars to changes in the mandibular dental arch. Am J Orthod Dentofacial Orthop. 1990 Apr;97(4):323-35.
In the majority of cases some degree of mandibular incisor crowding took place after retention, but this change was not significantly different between third molar subgroups. This finding suggests that the recommendation for mandibular third molar removal with the objective of alleviating or preventing mandibular incisor irregularity may not be justified.
Buschang PH, Shulman JD.
Incisor crowding in untreated persons 15-50 years of age: United States, 1988-1994. Angle Orthod. 2003 Oct;73(5):502-8.
We conclude that (1) approximately 50% of individuals in the United States who were 15-50 years of age have little or no mandibular incisor irregularity, 23% have moderate mandibular incisor irregularity, and 17% have severe irregularity, (2) erupted third molars are not associated with increased crowding, (3) crowding increases most during early adulthood, and (4) although individual differences in crowding are multifactorial, the primary determinants remain unidentified.
Little RM.link
Stability and relapse of mandibular anterior alignment: University of Washington studies. Semin Orthod. 1999 Sep;5(3):191-204.
Third molar absence or presence, impacted or fully erupted, seems to have little effect on the occurrence or degree of relapse.
Harradine NW, Pearson MH, Toth B
The effect of extraction of third molars on late lower incisor crowding: a randomized controlled trial. Br J Orthod. 1998 May;25(2):117-22.
The principal conclusion drawn from this randomized prospective study is that the removal of third molars to reduce or prevent late incisor crowding cannot be justified.
Samspon WJ.
Current controversies in late incisor crowding. Ann Acad Med Singapore. 1995 Jan;24(1):129-37.
Although the terminology is mildly controversial, late incisor crowding (tertiary crowding, late secondary crowding, post-adolescent crowding) is widely regarded as a normal maturation event which is likely to affect most individuals to some extent. Disagreement arises when attempts are made to quantify the change and to predict the timing of the crowding. Most young adults experience some degree of loss of incisor alignment, usually near the anticipated emergence time for the third molars, and almost characteristically it is the lower anterior teeth which best demonstrate the phenomenon. Unfortunately, the physiological crowding changes are frequently confused with orthodontic treatment relapse. Greater controversy surrounds the aetiology of the undesirable crowding changes and despite many attempts we are still not in the enlightened position of explaining, predicting or preventing the problem (except by permanent retention). It is illogical to assume a single cause as the beguilingly simple observation of crowding belies the complexity of possible interacting factors. Perhaps it is a capricious combination of: tooth size and arch form; facial growth pattern (differential soft tissue and skeletal maturation); continuing late growth rotations; cumulative effects of resting, functional and parafunctional soft tissue pressures; lack of compensating attrition; and an ill-defined, mesially acting force emanating from the back of the dental arch. Many theories have attempted to resolve the mystery of the mesially acting force, including: pressure from erupting third molars; an inherent mesial migration; continuing mesial and occlusal dental drifting; maturation and contraction of periodontal soft tissues (particularly the transseptal fibres); the anterior component of occlusal forces; and the lower anterior arch contracting influence of the incisor overbite.
White RP Jr, Madianos PN, Offenbacher S, Phillips C, Blakey GH, Haug RH, Marciani RD.
Microbial complexes detected in the second/third molar region in patients with asymptomatic third molars. J Oral Maxillofac Surg. 2002 Nov;60(11):1234-40.
In periodontally healthy young adults clinical and microbial changes associated with the initiation of periodontitis (gum disease) may present first in the third molar region in young adults.
Peng KY, Tseng YC, Shen EC, Chiu SC, Fu E, Huang YW.
Mandibular second molar periodontal status after third molar extraction. J Periodontol. 2001 Dec;72(12):1647-51
In this study, greater periodontal breakdown, including probing depth, attachment loss, and radiographic alveolar bone loss, was found at the distal (toward the back) sites, but not at the mesial (front surface) sites, of the experimental molars where the third molar was surgically extracted compared with the control teeth (no surgery). In the experimental molars, more radiographic bone loss was found at the sites adjacent to the surgical location than at the sites distant to the surgical location. Therefore, we suggest that the surgical removal of the mandibular third molar may lead to a periodontal breakdown on the distal surface of the second molar.
Kan KW, Liu JK, Lo EC, Corbet EF, Leung WK.
Residual periodontal defects distal to the mandibular second molar 6-36 months after impacted third molar extraction. J Clin Periodontol. 2002 Nov;29(11):1004-11.
The results suggest that periodontal breakdown initiated and established on the distal surface of a mandibular second molar in the vicinity of a ‘mesio-angular’ impacted third molar, evidenced by pre-extraction crestal radiolucency in association with inadequate plaque control after extraction, can predispose to a persistent localized periodontal problem.
Nemcovsky CE, Libfeld H, Zubery Y.
Effect of non-erupted 3rd molars on distal roots and supporting structures of approximal teeth. A radiographic survey of 202 cases. J Clin Periodontol. 1996 Sep;23(9):810-5.
Non-erupted tooth apical position and mesio-inclination of 60 degrees or more relative to the distal root of the second molar were significantly associated with root resorption (p = 0.01368 and p = 0.0194, respectively). Resorption was positively associated with age of patient (p = 0.00606). These results may support early extraction of impacted 3rd molars especially in cases with a mesio-angulation of 60 degrees or more and an apical location in proximity to the distal root of the 2nd molar.
Kugelberg CF.
Impacted lower third molars and periodontal health. An epidemiological, methodological, retrospective and prospective clinical, study. Swed Dent J Suppl. 1990;68:1-52.
The results two years postoperatively showed a higher prevalence of plaque, gingivitis and periodontal pockets on the distal surface of M2 than on other surfaces of the two molars adjacent to the extraction site. Infrabony defects greater than or equal to 4 mm were registered in 32.1% of the cases. The improvement concerning postoperative IBD, between the two examinations, was mainly seen in individuals less than or equal to 25 years of age. No case in this age group increased in depth, while 29.6% of postoperative IBD deteriorated in individuals greater than or equal to 26 years.
Elter JR, Offenbacher S, White RP, Beck JD.
Third molars associated with periodontal pathology in older Americans. J Oral Maxillofac Surg. 2005 Feb;63(2):179-84.
A visible third molar was associated with 1.5 times the odds of PD5+ on the adjacent second molar, while controlling for other factors associated with the presence of third molars and periodontal disease. Other factors positively associated with PD5+ in the model were male gender, older age, smoking, and irregular and episodic dental visits. The finding of more severe periodontal conditions associated with visible third molars in these middle-aged and older adults indicates that third molars may continue to have a negative impact on periodontal health well into later life.
Nieri M, Muzzi L, Cattabriga M, Rotundo R, Cairo F, Pini Prato GP.
The prognostic value of several periodontal factors measured as radiographic bone level variation: a 10-year retrospective multilevel analysis of treated and maintained periodontal patients. J Periodontol. 2002 Dec;73(12):1485-93.
Within the scope of this study design, many traditional prognostic factors were ineffective in predicting future bone level variation and therefore were of no prognostic value. Conversely, a few specific factors at each level emerged as valuable prognostic factors. At the patient level, the prognostic factor was initial mean bone level in conjunction with a positive IL-1 genotype. At the tooth level, the prognostic factor was tooth mobility. At the site level, the significant prognostic factors were initial bone level at a site, the infrabony component of a defect, and initial probing depth at a site. The use of these factors may be of value to clinicians as predictors of bone level variation when assigning a prognosis to a patient, a tooth, or a site.
Kugelberg CF.
Periodontal healing two and four years after impacted lower third molar surgery. A comparative retrospective study. Int J Oral Maxillofac Surg. 1990 Dec;19(6):341-5.
Two years postoperatively, 16.7% of the cases aged less than or equal to 25 years showed intrabony defects exceeding 4 mm, compared with 40.7% in the age group greater than or equal to 26 years. At the 4-year re-examination, the corresponding figures were 4.2% and 44.4%, respectively. The improvement concerning the alveolar bone level was mainly seen in individuals under 25 years.
Kugelberg CF, Ahlstrom U, Ericson S, Hugoson A, Kvint S.
Periodontal healing after impacted lower third molar surgery in adolescents and adults. A prospective study. Int J Oral Maxillofac Surg. 1991 Feb;20(1):18-24.
Early removal of impacted lower 3rd molars with large angulation and close positional relationship to the adjacent 2nd molar proved to have a beneficial effect on periodontal health.
Northway Orthodontics