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The Shortened Dental Arch by Dr. Tim Goodheart

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Categories: Prosthodontics;
The Shortened Dental Arch 

A treatment option for the partially edentulous patient

by Dr. Tim Goodheart

“But, doctor, how important is that tooth, actually?” “Do I really need to spend this much to keep this tooth? What if we just pull it?” “The teeth I’m missing: Do I need to fill those spaces?”

Every clinician has heard these words—many of us even before we graduated dental school.

The past 15–20 years have given dentists a tremendous boon in the ability to replace missing or nonrestorable teeth with the three familiar options of implants, traditional fixed bridges or removable partial dentures. But implant restorations and fixed bridges are often costprohibitive or undesirable for many patients, eliminating them as options. Removable partials, meanwhile, are often among the most frustrating treatment for dentists to provide and also often difficult for patients to adapt to wearing.

As clinicians, we know intuitively and from our daily clinic experiences that while the loss of a tooth, several teeth or even all teeth will change someone’s quality of life, it does not endanger life. As a removeable clinic instructor I had in dental school would say, “No one ever died because of a lack of teeth. People will figure out a way to eat enough to stay alive.” Yet for dentists, the traditional approach is to replace missing teeth.

Our education and training is geared toward “the three R’s”: rescuing teeth, and if they can’t be rescued, then removing and replacing them. Regardless of what the patient ultimately decides, this is typically at the center of our thought processes as we work through treatment planning. In fact, many years ago, Levin used the phrase “28-tooth syndrome” to describe the traditional belief in dentistry that 28 or more teeth, whether natural or replacement, would be the unofficial “correct” number for a satisfactory dentition.

So, can we more adequately and confidently provide a decent answer for the patient question of, “Doctor, do I really need that tooth?”


The background
In 1981, the Dutch clinician Käyser mentioned the phrase “shortened dental arch” (SDA) to describe and evaluate missing teeth and begin to better answer that question.1 Prosthodontist M.M. Devan, meanwhile, has repeatedly been cited as saying many times it’s better to preserve what is left instead of replacing what has been lost—something that again dentists know both intuitively and from experience. Mohl in 1988 went so far as to call it “obsolete” to go to great effort and expense to maintain 28 teeth.2 Witter, Ramfjord et al. published studies showing that in a large majority of the time, “Patients felt that replacement of molars with free-end removeable partial dentures did not contribute to oral comfort” and that partials are a “common cause of iatrogenic periodontal disease and should beavoided.”3,4

It becomes difficult for us as clinicians to determine up from down at times. Fortunately, there is some data to help us as we make clinical decisions and discuss tooth loss issues with patients.

Ash and Ramfjord5 discussed a physiologically acceptable occlusion if it conformed and met the following principles:
  • Absence of active pathological processes.
  • Satisfactory function in chewing, swallowing and speech.
  • Variations of form and function.
  • Ability to adapt to structural changes.
While the principles of Ash and Ramfjord are correct, they seem a little mechanical. From a more practical view, what we’re really asking is:
  • Is there adequate biting, chewing, speech and aesthetics for the patient to function?
  • Assuming there is no current pathology of the temporomandibular joint (TMJ), are the joints at future risk?
  • Will there likely be durable occlusal stability?
So if a patient lacks some teeth but has satisfactory function and few or no major complaints about lost teeth, the question must be asked: How necessary is it to do anything additional for the patient, and what are the consequences if we don’t?


Does the shortened dental arch have a legitimate place in dentistry?
Under the classical definition of Käyser, SDA was defined as the loss of teeth distal to the second premolar. More loosely and practically defined, SDA would simply be considered as an intact anterior dentition but a reduced number of occluding pairs of posterior teeth. Fig. 1 shows a few examples of possible SDA scenarios, with OU meaning posterior “occluding units” or pairs.

Let’s look at what the literature can tell us about the three main characteristics: chewing and aesthetics, TMJ stability and occlusal stability.
Shortened Dental Arches
Fig. 1

Chewing and aesthetics
Käyser initially evaluated this issue in 1981 by using a chewing test based on the release of a light-absorbing material when chewing raw carrots. He determined that a decreased number of occlusal pairs, not surprisingly, required more chewing strokes but that the change was progressive—not sudden—with people having sufficient capacity to adapt to tooth loss and still eat satisfactorily.
  • Aukes et al.6 found that chewing with SDA groups is hindered but within an “acceptable degree,” with only small differences noted between variations of SDA and those with complete dental arches.
  • De Souza et al.7 mentioned studies in Tanzania and Brazil that also showed satisfactory and adequate ability to chew with the presence of all the anterior teeth plus three pairs of occluding premolars.
  • Witter et al.8 stated: “Shortened dental arches are not associated with shifts in food selection adversely affecting general health” provided that the patient has 20 or more “well distributed” teeth; only at the point of less than 10 pairs of occluding teeth do significant changes in food selection occur.
  • In a study from 2014, Singh et al.9 concluded that “SDA subjects can provide masticatory performance and patient satisfaction level within acceptable range to that of CDA (complete dental arch) subjects despite remarkable reduction in number of teeth and occlusal force.”
As to aesthetics: Situations are extremely variable and in general are determined by the patient and their own personal evaluation, regardless of what we may think. Käyser found that lower arch shortening did not raise any appreciable aesthetic problems for most patients. In the upper arch, shortening up to the second premolar would give a negative but acceptable evaluation of appearance by the patient; however, loss of either the first or second premolar was the point at which patients judged themselves negatively and would look for tooth replacement.

So from three-plus decades of data looking at SDA, it seems we can conclude that most people will physiologically adapt to posterior tooth loss and are able to chew acceptably and comfortably so long as approximately 10+ pairs of occluding teeth are present. At less than 10 pairs of occluding teeth, function starts to noticeably change.


SDA and TMJ risks
Now, what of the TMJ? Perhaps shortened dental arches will lead to joint overloading and/or pain.
  • Witter in 1994 concluded in a clinical trial study that loss of molars was not a risk factor for TMD.10
  • Hattori in 2003 measured bite force and masticatory muscle myelograms on people with appliances that created symmetrical SDA.7 The findings gave no evidence that SDA causes overloading of joints or teeth, suggesting that there is likely a self-regulatory system controlling maximum biting strength with various occlusal situations.
  • Sarita, also in 2003, studied 725 people with intact anterior regions and zero to eight occluding pairs posteriorly, comparing them to a control group of 125 people with completely intact arches.8 The test subjects were interviewed and examined regarding pain, sounds within the TMJ and restricted movement and opening. No evidence was found that SDA provoked signs or symptoms associated with TMD, but it was found that there was a measurable increase in risk for pain and joint sounds when all posterior support (all molars, all premolars) was absent.
  • In 2014, Reissman et al. completed a multicenter trial to assess the impact of missing posterior support and TMD pain by comparing patients with SDA with those with molar replacement with removeable partial.9 No difference among the two groups was found.
So in considering SDA and the TMJ, evidence again seems to point toward SDA not being associated with or a key risk factor in adequate and comfortable function of the joints.


Occlusal stability
Now to look at stability of the shortened arch.

In 1991 Witter et al.10 examined periodontal support in groups with SDA, those with complete arches and those with SDA and wearing free-end partials. Within that study, they found the differences between the three groups with regard to periodontal support were small, but an existing severe periodontal situation and SDA was unfavorable for long-term tooth survival.

Then, in 2001, Witter et al.11 again examined groups for occlusal stability indicators of:
  • Interdental spacing.
  • Occlusal contacts of anterior teeth in intercuspal position.
  • Overbite.
  • Occlusal tooth wear.
  • Alveolar bone support.
The researchers concluded that compared with complete dental arches, patients with SDA had similar overbite and wear. There was in the SDA group more interdental spacing in the premolar areas, more anterior teeth in contact and lower alveolar bone scores; however, the differences remained constant over time, indicating good long-term occlusal stability. Researchers concluded that “occlusal changes were self-limiting, indicating a new occlusal equilibrium.”

Sarita et al.12 in 2003 examined interdental spacing, occlusal contact of incisors and vertical overlap in SDA compared with complete dental arches. They concluded that there was indeed an increased risk in occlusal stability of these three factors in the “extreme” shortened arch (zero to two pairs of occluding premolars), but there was no evidence of increased risk in intermediate groups (three or more pairs of occluding premolars).


Discussion
Obviously, we all have patients with various patterns and occasions of missing teeth. Some we can restore back to full form, and for others that option is not possible.

There are—as in most things—advantages, disadvantages and criteria in considering SDA.

Advantages
  • Meets criteria for functional dentition.
  • Reduces the amount of restorative work, reducing costs and allowing patients to focus their financial resources.
  • Remaining teeth are more easily accessible for hygiene and maintenance, potentially enhancing their prognosis.
  • SDA can simplify complex treatment planning that may not be desired or understood by the patient.
  • Can help us in prevention of inadvertent overtreatment.
Disadvantages
  • Not all people can adapt to and accept a shortened dental arch.
  • SDA in conjunction with an existing periodontal disease is a significant risk factor for future loss of teeth.
  • Aesthetics are compromised, which will not meet the needs of all patients.
Criteria when considering SDA as a treatment option
  • Major problems (including decay, periodontal disease and severe tipping) occur, mainly in the molars.
  • Good prognosis of the anterior and premolar regions.
  • There are limited possibilities (finances, health concerns, patient desire) for more extensive restorative care.
  • Maintaining 10 or more “occluding pairs” is the mark that is associated with generally satisfactory function for most people. Fewer than 10 occluding pairs is often the beginning of more noticeable functional problems for the patient.
  • The patient is motivated to keep the remaining teeth.
Issues to be considered as possible contraindications for SDA
  • Intensive bruxism/parafunction.
  • Preexisting TMD.
  • Advanced periodontal disease.
  • Advanced pathological tooth wear and/or erosion of remaining teeth.
  • Patient under the age of 40.

Conclusion
For dentists, the drive to replace missing teeth in our patients can be a strong one. It’s one that comes with our education and training. The goal in looking at the SDA concept is not to suggest not replacing missing teeth—our ability to help patients regain full form and function after tooth loss has never had better materials and treatment options then available today. Rather, the goal is to help better understand in those cases when, for whatever reason, replacing missing teeth isn’t reasonable or possible, and just how a shortened dental arch concept might be of value and give us additional treatment option.

The literature and data have shown that a SDA of anterior with premolar/molar tooth combinations can and most often does fulfill the requirements for a satisfactory and functional dentition. Consideration as to patient needs, health and desires frequently leads us to determine that no additional dentistry may be the route of choice.

A planned case of shortened dental arches can provide for a cost-effective treatment with a functional and stable long-term dentition. The concept can be biologically sound—one in which we can be confident and positive—and deserves consideration as an option among others in treatment planning for the partially edentulous patient.

References
1. Käyser AF. Shortened dental arches and oral function. J Oral Rehabil. 1981 Sep; 8(5):457–62.
2. Mohl ND. A Textbook of Occlusion. Chicago: Quintessence Pub. Co, 1988.
3. Witter DJ, de Haan AF, Käyser AF, van Rossum GM. A 6-year follow-up study of oral function in shortened dental arches. Part I: Occlusal stability. J Oral Rehabil 1994 Mar; 21(2):113–25.
4. Ash MM, Ramfjord SP. Occlusion. W.B. Saunders Co., 1995.
5. Ibid.
6. Aukes JN, Käyser AF, Felling AJ. The subjective experience of mastication in subjects with shortened dental arches. J Oral Rehabil. 1998 July; 15(4):321–4.
7. de Souza R, Fedorowicz Z, Pedrazzi V. The shortened dental arch: An evidence-based treatment option. Smile Magazine [internet]. Accessed April 2, 2024. Available from: www.smile-mag.com/art_files/The_Shortened_ Dental.pdf.
8. Witter DJ, Cramwinckel AB, van Rossum GM, Käyser AF. Shortened dental arches and masticatory ability. J Dent. 1990 Aug; 18(4):185–9.
9. Singh M, Tripathi A, Raj N, Singh R. Evaluation of masticatory performance in subjects with shortened dental arch: A comparative study. Eur J Gen Dent. 2014 May–Aug; 3(2):146.
10. Witter DJ, De Haan AF, Käyser AF, Van Rossum GM. Shortened dental arches and periodontal support. J Oral Rehabil. 1991 May; 18(3):203–12.
11. Witter DJ, Creugers NH, Kreulen CM, de Haan AF. Occlusal stability in shortened dental arches. J Dent Res. 2001 Feb; 80(2):432–6.
12. Sarita PT, Kreulen CM, Witter D, Creugers NH. Signs and symptoms associated with TMD in adults with shortened dental arches. Int J Prosthodont. 2003 May–Jun; 16(3):265–70.

Additional reading
Alam M, Joshi S, Joshi P. Shortened dental arch: A simplified treatment approach. J Nepal Dent Assoc. 2014; 14:34–37.

Armellini D, von Fraunhofer JA. The shortened dental arch: A review of the literature. J Prosthet Dent. 2004 Dec; 92(6):531–5.

de Sa e Frias V, Toothaker R, Wright RF. Shortened dental arch: A review of current treatment concepts. J Prosthodont. 2004 Jun; 13(2):104–10.

Gerritsen AE, Witter DJ, Bronkhorst EM, Creugers NH. An observational cohort study on shortened dental arches—clinical course during a period of 27–35 years. Clin Oral Investig. 2013 Apr; 17(3):859–66.

Kanno T, Carlsson GE. A review of the shortened dental arch concept focusing on the work by the Käyser/Nijmegen group. J Oral Rehabil. 2006 Nov; 33(11):850–62.

Hattori Y, Satoh C, Seki S, Watanabe Y, Ogino Y, Watanabe M. Occlusal and TMJ loads in subjects with experimentally shortened dental arches. J Dent Res. 2003 Jul; 82(7):532–6.

Reissmann DR, Heydecke G, Schierz O, Marré B, Wolfart S, Strub JR, Stark H, Pospiech P, Mundt T, Hannak W, Hartmann S, Wöstmann B, Luthardt RG, Böning KW, Kern M, Walter MH. The randomized shortened dental arch study: Temporomandibular disorder pain. Clin Oral Investig. 2014 Dec; 18(9):2159–69.

Author Bio
Tim Goodheart Tim Goodheart, DDS, MBA, FAGD, has owned a private practice in Raytown, Missouri, since 1994. After graduating from the University of Missouri—Kansas City School of Dentistry, Goodheart completed a general practice residency at the VA Medical Center in Kansas City. He also earned an MBA from the Oklahoma State University Spears School of Business.
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