Download Enigma of Class II molar finishing. (PDF Available)

American Journal of Orthodontics and Dentofacial Orthopedics
Volume 126, Number 6
experience, it is doubtful that patients treated with spaceopening and prosthetic replacements will have better longterm treatment results than those treated with orthodontic
space closure. The question to be answered by controlled
clinical studies in the future will be: what is preferable in a
life-long perspective for the patient, either a natural “living”
root or an ankylosed foreign body in the site of the missing
maxillary lateral incisor?
In this letter, we have focused on the permanence of
replacements for missing maxillary lateral incisors. Treatment
decisions for young people with missing incisors should be
based on a comprehensive assessment that includes many
factors.14 For many patients, the best results can be obtained
by an interdisciplinary approach including implants or cantilever prosthetics. The challenge is, however, to plan treatment
according to the patient’s needs and diagnosis, and not on the
assumption that implants are superior to orthodontically
positioned and reshaped natural teeth.
Bjorn U. Zachrisson, DDS, MSD, PhD
Arild Stenvik, DDS, MSD, PhD
Oslo, Norway
0889-5406/$30.00
doi:10.1016/j.ajodo.2004.10.006
REFERENCES
1. Turpin DL. Treatment of missing lateral incisors. Am J Orthod
Dentofacial Orthop 2004;125:129.
2. Wilson TG Jr, Ding TA. Optimal therapy for missing lateral
incisors? Am J Orthod Dentofacial Orthop 2004;126(3):22A23A.
3. Thilander B, Odman J, Lekholm U. Orthodontic aspects of the
use of oral implants in adolescents: a 10-year follow-up study.
Eur J Orthod 2001;23:715-31.
4. Iseri H, Solow B. Continued eruption of maxillary incisors and
first molars in girls from 9 to 25 years studied by the implant
method. Eur J Orthod 1996;18:245-56.
5. Oesterle LJ, Cronin RJ Jr. Adult growth, aging, and the singletooth implant. Int J Oral Maxillofac Implants 2000;15:252-60.
6. Chang M, Wennström JL, Odman P, Andersson B. Implant
supported single-tooth replacements compared to contralateral
natural teeth. Crown and soft tissue dimensions. Clin Oral Impl
Res 1999;10:185-94.
7. Tuverson DL. Close space to treat missing lateral incisors. Am J
Orthod Dentofacial Orthop 2004;125(5):17A.
8. Rosa M, Zachrisson BU. Integrating esthetic dentistry and space
closure in patients with missing maxillary lateral incisors. J Clin
Orthod 2001;35:221-34.
9. Weichbrodt DJ, Stenvik A, Haanæs HR. An intra-individual
evaluation of implant supported single tooth replacements for
missing maxillary incisors (abstract). 18th Congress of the Nordic
Association of Orthodontists, Loen, Norway, September 4-7,
2003.
10. Thordarson A, Zachrisson BU, Mjör IA. Remodeling of canines
to the shape of lateral incisors by grinding: a long-term clinical
and radiographic evaluation. Am J Orthod Dentofacial Orthop
1991;100:123-32.
11. Wennström J. Personal communication 2004.
12. Esposito M, Ekestubbe A, Gröndahl K. Radiological evaluation
of marginal bone loss at tooth surfaces facing single Brånemark
implants. Clin Oral Impl Res 1993;4:151-7.
13. Andersson B, Odman P, Lindvall AM. Single-tooth restorations
Readers’ forum 15A
on osseointegrated implants: results and experiences from a
prospective study after 2-3 years. Int J Oral Maxillofac Implants
1995;11:311-21.
14. Stenvik A, Zachrisson BU. Orthodontic closure and transplantation in the treatment of missing anterior teeth. An overview.
Endod Dent Traumatol 1993;9:45-52.
Enigma of Class II molar finishing
The orthodontic literature, from the days of Bolton,1
contains ample articles about correction of the anterior
segment, with the molars finished in a Class II relationship.
Particularly noteworthy are the patients with Class II
malocclusions who are treated with extractions only in the
maxillary arch. In a well-written thesis, Kessel2 argued
that, in nongrowing patients (above 12 years) with a
particular type of Class II malocclusion, single-arch extraction is a justifiable method of treatment. Standard
textbooks like those of Bishara3 and Proffit4 also document
cases in which the molars were left in a Class II relationship at the end of the treatment. A recent article in the
AJO-DO, “Class II treatment success rate in 2- and
4-premolar extraction protocols” (Janson G, Brambilla AC,
Henriques JFC, de Freitas MR, Neves LS. Am J Orthod
Dentofacial Orthop 2004;125:472-9), compares Class II
patients treated with single-arch and both-arch extractions
and concluded that the former was better.
What intrigues me is that, for a century, we orthodontists have made the correction of Class II molar relationships a top priority. Whether we used a myofunctional
approach, comprehensive fixed appliances, or even surgical treatment, finishing with the molars in a Class I
relationship was considered almost mandatory. But were
we chasing the wrong treatment goal? Was Angle wrong in
assigning a malocclusion label to the Class II molar
relationship? Is the first part of Andrews’ first key to
normal occlusion worth ignoring?
As a great admirer of tooth size and morphology in
relation to malocclusion and treatment results, I find it very
difficult to accept Class II molar finishing.
Bolton’s tooth size ratio has shown us that proper
maxillary and mandibular tooth size and proportion are
essential for a normal occlusal relationship. The importance
of the anterior ratio is well understood and applied clinically.
In essence, 3 maxillary anterior teeth occlude with 3.5
mandibular anterior teeth in each quadrant for a normal
anterior relationship—ie, overjet, overbite, and midline. It can
also be interpreted that maxillary anterior teeth in the outer
arc have a larger mesiodistal dimension than the mandibular
ones. The size of anterior teeth in normal circumstances is
designed to give overjet, overbite, midline, and canine occlusion.
It is possible to extrapolate a similar posterior ratio from
the overall ratio of Bolton. From the 77% anterior ratio,
mandibular teeth (first molar to first molar) pick up to become
91% value in the overall ratio. Logically and factually, the
mandibular posterior teeth are larger mesiodistally than the
maxillary posteriors. Five maxillary posterior teeth (first
16A Readers’ forum
premolar to third molar) occlude with 4.5 mandibular posterior teeth when third molars are present. If the third molars are
not considered, 4 maxillary posterior teeth (first premolar to
second molar) occlude with 3.5 mandibular posteriors. Because the shape of the posterior arch is not an arc, maxillary
teeth might not require extra arch length. Nature’s design of
posterior tooth size agrees with normal (Class I) intercuspation for balanced functioning as the best form-and-function
interrelationship.
In Class II malocclusion, a distal step at the posterior end
of the occlusion is the least desirable goal of orthodontics, and
also Class III with a mesial step at the distal end.
With this background in mind, if we analyze Class II
molar relationships, it will be seen that the distal half of the
mandibular third molars (if present) or the distal half of the
mandibular second molars will have no functioning occlusal
contact. This can be verified clinically if we see the distal end
of occlusion carefully and verify study models for the same.
Thus, it can be conclusively shown that a Class II molar
relationship is not tenable morphologically.
Kessel’s argument2 stops at the mesial cusp of the
maxillary first molar without looking beyond it. But out of
sight can’t be out of mind. At the start of his thesis, Kessel
also elaborates on the difficulty of correcting Class II molar
relationships, subscribing to the “if you can’t beat ‘em, join
‘em” policy. Kessel’s arguments, at best, are compromises.
Correcting only the visible components of malocclusion—ie,
overjet and proclination, and leaving behind proper intercuspation of the posterior teeth—is not becoming of a professional orthodontist. As guardians of occlusion, orthodontists
cannot leave the large distal half of a mandibular molar
without occlusal contact in centric occlusion.
Let the experts in functional occlusion and gnathology
comment on the implications of only the mesial half of the
mandibular second molar having an occluding antagonist
while the distal half is left nonfunctional. It might not
supraerupt, but equilibrium and stability are the questions.
Far-reaching implications of an imbalanced posterior occlusion on TMJ function must be explored.
It may be one thing to accept Class II molar finishing in
compromised, mutilated, or adult orthodontic patients. But
eliminating molar Class II correction from the treatment
objectives altogether goes against century-old orthodontic
teaching and preaching. The current implication of “better
occlusal success rate” (with a 2-premolar extraction “protocol” than with 4 premolar extractions) Class II molar finish
stretches the limit a step further. Left unquestioned, in the
next decade, we might see “attainment of Class II molar
relationship” as a desirable treatment objective!
Class II molar relationships are not tenable morphologically or physiologically. Our illustrious predecessors couldn’t
have been wrong in spending maximum energy and strategy
in trying to resolve them.
Jayaram Mailankody, MDS
Calicut, Kerala, India
0889-5406/$30.00
doi:10.1016/j.ajodo.2004.10.007
American Journal of Orthodontics and Dentofacial Orthopedics
December 2004
REFERENCES
1. Bolton WA. Clinical applications of a tooth size analysis. Am J
Orthod 1962;48:504-29.
2. Kessel SP. The rationale of maxillary premolar extraction only in
Class II therapy. Am J Orthod 1963;49:276-93.
3. Bishara SE. Textbook of orthodontics. Philadelphia: W. B. Saunders/Harcourt; 2001. p.359.
4. Proffit WR. Contemporary orthodontics. 3rd ed. Saint Louis:
Mosby/Harcourt; 2000. p. 274.
Author’s response
Thank you for your comments and for sharing your
perspectives on our article, “Class II treatment success rate
in 2- and 4-premolar extraction protocols.” Because a
debate is suggested, I would like to answer some of your
concerns.
Were we chasing the wrong treatment goal? No, we
were chasing the right treatment goal for that time in Class
II malocclusion cases. Initially, it was thought and taught
that molars should always finish in a Class I relationship.1-5 Later, many orthodontists realized and researchers
proved that, in some Class II malocclusions, the molars
could be finished in a Class II relationship without unfavorable collateral effects.6-11 Enough clinical and scientific
evidence has been provided to support finishing treatment
of certain Class II malocclusions with molars in a Class II
relationship.
Was Angle12 wrong in assigning a “malocclusion” label
to the Class II molar relationship? No, Angle was not
wrong—if a full complement of teeth is present in an
untreated natural denture or the corresponding dental units
have been extracted in both dental arches.
Is the first part of Andrews’ first key to normal occlusion
worth ignoring? No, not when the treatment plan involves
finishing with the molars in a Class I relationship. This is the
treatment goal when treating nonextraction13 or when treating
by extracting corresponding dental units in both arches.14,15
However, if the treatment plan consists of only 2 maxillary
premolar extractions, the molars will finish in a Class II
relationship.16 This is nowadays so widely accepted that
Andrews has designed a first maxillary molar tube with
specific rotation to perfectly fit into a Class II molar relationship at the end of treatment.16,17
Additionally, there is no evidence in the literature that
finishing with a Class II molar relationship has any implications for treatment stability18-20 and TMJ problems.21-27
Our findings showed that a 2-premolar extraction protocol in complete Class II malocclusions provided a better
occlusal success rate than a 4-premolar extraction protocol,
but this by no means suggests eliminating Class II molar
correction in every situation. Rather, the findings demonstrate
that the 2 maxillary-premolar extraction protocol in complete
Class II malocclusions, in general, provides a better occlusal
success rate because it depends less on patient compliance, as
previously suggested.6,17 Therefore, it alerts the orthodontist
to the great difficulty of the 4-premolar extraction approach in