Hemisections
Facilitating the orthodontic correction of lower second premolar agenesis.
Agenesis
1) Baccetti, T., "A Controlled study of associated dental anomalies," AO, 1998, 68(3), 267-74
- 100 individuals each with one (or more) of the following anomalies were compared to 1,000 controls
- A correlation was demonstrated at a significance level of p<.005 for 5 anomalies:
- Aplasia of second premolars
- Reduced size of maxillary lateral incisors
- Palatally displaced maxillary canines
- Infraocclusion of primary molars
- Enamel hypoplasia
There appears to be a genetic origin, and the presence of any one such reciprocal association should indicate the increased risk for others.
2) Baccetti, T, "A clinical and statistical study of etiologic aspects related to associated tooth anomalies in number, size and position," Minerva Stomatol, 1998, 47(12): p 655-63
Demonstrates a lack of correlation between ectopic eruption of first molars and four factors which do bear statistical association: aplasia of second premolars, reduced size of maxillary lateral incisors, infraocclusion of primary molars and palatally displaced canines.
3) Baccetti, T "Tooth anomalies associated with failure of eruption of first and second molars," AJODO, 2000, 118(6), p 608-610
- Seven groups of affected individuals with 100 subjects each was compared with a control of 1520
- Failures in eruption of first and second molars were correlated with positional anomalies: palatally displaced maxillary canines, infraocclusion of primary molars and rotated maxillary lateral incisors. They could not be associated with developmental anomalies: aplasia of second premolars, reduced size of maxillary lateral incisors, and enamel hypoplasia.
- There appear to be two separate genetic disturbances, the former being somehow connected to alveolar bone or periodontal ligament metabolism.
4) Brook, AH, "A unifying aetiological explanation for anomalies of human tooth number and size," Arch Oral Biol, 1984, 29(5), p 373-8
When looking at relatives of people who has supernumerary teeth, hypodontia, megadontia and microdontia, there was a very highly significant increase in frequency for all anomalies. Males more often had supernumerary teeth and megadontia and females more frequently hypodontia and microdontia.
5) Davis, PJ (1987) 1093 children from Southern China - age 12:
- 6.1% males had agenesis (excluding 3rd molars)
- 7.7% females (6.9% of total sample).
- 58.7% of affected children were missing lower incisor(s).
6) Daugaard-Jensen J, et al, "Pattern of agenesis in the primary dentition: a radiographic study of 193 case," Int J Peadiatr Dent, 1997, 7(1), 3-7
An interesting review of the frequency and sequelae of agenesis of primary teeth
7) Daugaard-Jensen J, et al, "Comparison of the pattern of agenesis in the primary and permanent dentitions in a population characterized by agenesis in the primary dentition," Int J Paediatr Dent, 1997, 7(3), 143-8
A review of the succession of agenesis into the permanent dentition: agenesis of a primary incisor was often but not always followed by agenesis of the succedaneous tooth. In the molar region, agenesis of a primary tooth was in all cases but one followed by agenesis of the succedaneous tooth.
8) Garn, S.M. "Genetics of dental development," The Biology of Occlusal Development, Monograph #7,Craniofacial Growth Series, CHGD, Ann Arbor,1977
- Genetic control mechanisms work along gradients involving reductions in tooth number, tooth size, rates of formation and formation sequence
- When M3 is congenitally missing other teeth tend to be missing, generally the more distal in each morphological class: most likely P2, M2, I2
- These gradients work from the back forward with size reduction, and from the front backward as it applies to developmental delays.
9) Grahnen, H, "Hypodontia in the permanent dentition, Odontol.Revy, 1956, 7 (suppl #3), p. 1-100.
10) Kotsomitis et al (1996) 101 pairs of twins found 8.4% with agenesis
11) Lai, PY and Seow, WK (1989) investigating 1032 children with hypodontia associate it with ankylosed primary molars 65.7% of the time, taurodontism of mandibular molars 34.3%, enamel hypoplasia 11.9% and conical incisors 8.9%
12) Markovic, M (1982) 165 pairs of twins
- 4.8% were missing maxillary lateral incisors
- 3% were missing lower second premolars
13) Nodal, M., et al. "Craniofacial morphology in patients with multiple congenitally missing teeth," Eur.J.Orthod, 1994: 16: 104-9
Divided groups according to number of CMT: 5-12 vs. 13-21
( No significant correlations between number of missing teeth and cephalometric variables within groups.
( Between group comparisons were significant with the larger group having:
- reduced mandibular plane angle (SN-MP)
- reduced gonial angle (Ar-Go / MP)
- more prognathic mandible (S-N-Po)
It is suggested that the differences are due to reduced vertical development of the lower face, caused by reduced occlusal support.
14) Øgaard,B and Krogstad,O. "Craniofacial structure and soft tissue profile in patients with severe hypoplasia," Eur.J.Orthod, 1994: 16: 104-9
Divided groups according to number of CMT: I. 2-5 II. 6-9 III. >9
( In group 1, lower second premolars were most commonly lost, followed by upper second premolar, then upper laterals.
* The relative frequency of missing second premolars diminishes with increased increasing severity of hypoplasia
* Group III differed significantly in greater retroclination of lower incisors, increased interincisal angle, retracted lip profile, and reduced vertical dimension (FMA and ANS-Gn).
* This "flattening" was thought to be due to dental and functional compensation rather than to a different growth pattern
15) Peck, Peck and Kataja, "Prevalence of tooth agenesis and peg-shaped maxillary lateral incisor associated with palatally displaced canine (PDCP) anomaly," AJODO, 1996,110(4), p 441-443.
- 58 nonsyndromic N.A. orthodontic patients
- There is a much greater likelihood that maxillary canines will be palatally displaced in cases with agenesis of M3 or P2, and there's a greater likelihood of peg-shaped laterals.
Agenesis of maxillary laterals was not correlated with PDC.
16) Rose (1996) from 6000 orthodontic patients found 4.3% to be missing teeth
17) Thongudomporn, U (1998) from 111 orthodontic patients, 8.1% presented with agenesis
- Van der Linden (1983) Development of the Dentition
- the third molar is most frequently not formed (16%)
- next the mandibular second premolar (4.4%)
- maxillary lateral (1.7%)
- maxillary second premolar (1.6%).
Alveolar atrophy
1) Ostler, S., Kokich, V. "Alveolar ridge changes in patients congenitally missing mandibular second premolars." J Prosth D, 199471(2), p.144-9
- 22 patients -- 35 edentulous spaces
- 25% reduction in width in first 3 years
- 4% more over the next 3 years
- 2% reduction in ridge height
- No correlation between changes in height and width and the time since extraction or the age of the patient at the time of extraction.
Extraction Versus Non-Extraction
1) Komolpis, R.P., "Cephalometric comparison between first premolar and second premolar extraction," Thesis: U. Mich., 1998
- Discriminant analysis was used to select sub-samples of cases treated by first and second lower second premolar extraction, respectively. These differed in FMA, mandibular position, incisor position, and upper Z angle.
- The only skeletal changes were an increase in face height and forward translation of the mandible in the first premolar cases
- The treatments produced statistically similar incisor retraction and profile change
Development
1) Johnston, Lysle E, "Balancing the books on orthodontic treatment: an integrated analysis of change, Brit J. Orthodontics, 1996, 23, pp. 93-102. An explanation of the development of the "Pitchfork Diagram."
2) Johnston, Lysle E. "Growth and the Class II Patient: Rendering unto Caesar," Seminars in Orthodontics, 4 (1), 1998, pp59-63. A method of "factoring out good growth" when evaluating the actual contribution of any given treatment modality on the changes that take place in the face during treatment, as opposed to that which might have taken place without treatment.
3) Kieser, Julius, Human Adult Odontometrics, Cambridge University Press, Cambridge, 1990
4) Moyers, RE, et al, Standards of Human Occlusal Development, Monograph #5, Craniofacial Growth Series, CHGD, Ann Arbor,1976
5) Riolo, ML, et al, An Atlas of Craniofacial Growth: Cephalometric standards from the University School growth study, The University of Michigan,Craniofacial Growth Series, CHGD, Ann Arbor,1974
Hemisections
1) Buhler, H, "Survival rates of hemisected teeth: an attempt to compare them with survival rates of alloplastic implants," Int J Perio Rest Dent, 1994, 14(6), 536-43
- The compiled results of studies on hemisection revealed an average reported failure rate of 13.1%
- This failure rate was compared with that of implants; "the failure rates of the two treatment alternatives are not substantially different."
- Compares cost, simplicity and success rate.
2) Van der Linden, F.P.G.M., Problems and procedures in Dentofacial Orthopedics, Quintessence, 1990
Statistics
1) Kirk, Roger E., Statistics: an Introduction, 3rd. Edition, Holt, Rinehart and Winston, Inc, Orlando, 1990