Anterior Guidance: Myth or Mandatory?
An examination of the role the anterior teeth play in occlusal stability
What causes teeth to wear? Why can some patients go through life with almost no signs of “attrition,” whereas others have exposed dentin in their early 20s? Why do some front teeth become loose in the absence of periodontal disease? Why do diastemas appear without any apparent reason between brand-new crowns that look absolutely beautiful? Why do other brand-new, esthetic anterior crowns fracture or debond? What specific role do the anterior teeth play in creating a stable occlusion?
Arguments continue to persist about how a dentist should design the lingual contours of the maxillary anterior teeth for maximum results. Some dentists advocate the creation of a steep enough path (anterior guidance) to make sure the posterior teeth disclude, carefully checking the patient’s mandibular movements as the jaw moves “inside out.” Other camps maintain that wear and dysfunction occur when the anterior guidance is too steep, so they carefully check the path of the mandibular incisors as the jaw functions “outside in,” verifying that there is no inappropriate horizontal load. So the debate continues. Does the damage occur as the mandible travels inside out, or does it happen when the mandible travels outside in? Or is it possible that it is necessary to create contours that are in harmony with both movements? This discussion examines the role the anterior teeth play in occlusal stability and illustrates sound occlusal goals through a case report.
The Two Jobs of the Anterior
Be Steep Enough to Disclude the Posterior Teeth
After creating stable centric stops in centric relation (CR), nothing is more important than preventing the back teeth from rubbing. Landmark electromyographic research by Williamson and Lunquist1 in 1983 clearly showed the dramatic increase in muscle activity when back teeth rub. Bruxing is an “inside-out” movement.2 In fact, it is rare to find worn incisors or canines without the presence of a posterior interference. Additional research by Kerstein further supports the simple fact that the rubbing of posterior teeth during excursions will increase muscle activity and create damage to the system.3,4
If complete control of the masticatory system is to be assured, it is critical to have an anterior guidance steeper than the posterior morphology. This will allow for the least amount of muscle activity when the patient’s teeth are moving through the excursive movements, ultimately removing damaging stress from the posterior and anterior teeth.
Be in Harmony with the Envelope of Function
The literature clearly supports the importance of creating posterior disclusion; however, it is definitely possible to make the anterior guidance too steep. If the lingual contour of the maxillary anterior teeth is steeper then the outside-in path the lower incisors travel during chewing or speaking, pathology will follow.5,6 This pathology can manifest itself as mobility, migration (diastemata-appearing), wear, fracture, or restorations popping off. Stated another way, the lingual contour of the maxillary anterior teeth must be in complete harmony with the precise path the mandible follows during chewing or speech.
The Concept of a Customized Anterior Guidance
In the first edition of his book Evaluation, Diagnosis and Treatment of Occlusal Problems, Dawson discussed the concept of a customized anterior guidance,7 and that an anterior guidance would be incorrect if it did not provide for both of the criteria previously discussed. For the anterior teeth to be comfortable, as well as to do their part in creating an optimal occlusion, the lingual contour of the maxillary anterior teeth must be steep enough to disclude the posterior teeth and be in harmony with the envelope of function.
Case Presentation
A 51-year-old man diagnosed with mild sleep apnea who had not been compliant with a CPAP machine was referred to the practice by a physician (Figure 1 through Figure 3). The physician wanted a sleep apnea orthotic fabricated in hopes of obtaining better compliance. When the patient contacted the office, he expressed interest in having his smile enhanced as well.
Upon a complete examination, he was found to have moderate wear into dentin on teeth Nos. 6 to 11 and Nos. 22 to 27 (Figure 4 through Figure 7). The superficial masseters, right temporalis, and medial pterygoid muscles were tender to palpation (Figure 8). He reported two to three headaches per week. He had no history of tempomandibular joint (TMJ) pain, popping, clicking, or dysfunction. His range and path of motion were within normal limits, and his joints were loadable, without any sign of tension or tenderness in either joint.
Examination of the occlusion revealed a large slide between CR and maximum intercuspation (MI), with the first point of contact between teeth Nos. 2 and 31. Bilateral balancing interferences on the second molars resulted in the canines not being able to disclude the balancing side during excursive movements. When the canines came into contact on the cusp tips, the back teeth rubbed together. This is a very common yet often missed occurrence that a thorough occlusal examination can reveal.
The complete examination included a full periodontal charting (no probing depth greater then 3 mm, with mild localized gingivitis), a full restorative charting, a full-mouth series of x-rays, a full series of diagnostic photographs, and mounted diagnostic casts in CR.
The Treatment Plan
The goal of this treatment plan was to create long-term biologic and functional stability, an attractive smile, and to fit the patient for a sleep apnea appliance. Biologically, the patient needed two appointments with the hygienist and replacement of two older amalgams (teeth Nos. 2 and 30). Functionally, to create an optimal occlusal scheme—centric stops on all teeth, anterior guidance in harmony with the envelope of function, and non-interfering posterior teeth—the patient needed an equilibration combined with restorations on the anterior teeth.
Additionally, this patient needed to be fitted with a sleep apnea appliance. The challenge was to determine the proper point in the treatment plan for delivering the sleep apnea appliance. While the appliance had to be a very high priority due to the medical issues associated with sleep apnea, some studies indicate the occlusion may change after the placement of such an appliance. So how should a case like this be sequenced?
Sequencing for Success
The author recommends adhering to the following sequence of steps, which is executed in three stages.
Stage 1: Biologic Stability
The goal in this stage is to address biologic stability and correct all issues related to infection, caries, or periodontal disease.
This patient required only the following:
• Periodontal scale due to inflammation
• Periodontal prophy
• Home care instructions to help improve hygiene
• Replacement of degraded amalgam restorations (teeth Nos. 2 and 30) with resin
Stage 2: Functional Stability
The goal in this stage is to address functional stability, so the clinician creates, tests, and verifies occlusal stability.
For this patient, this involved:
• Occlusal equilibration (reductive on the posterior teeth) to eliminate the slide (Figure 9)
• Additive equilibration (resin composite on the incisal edges of teeth Nos. 6-11, Nos. 22-27) to restore anterior guidance (Figure 10)
• Delivering the sleep apnea appliance (Figure 11)
It is important to remember that once the patient is biologically and functionally stable, the definitive porcelain restorations can be phased in if financial constraints preclude having all work completed at once (which was the case with this patient). Phasing the definitive restorations in this case also offered the opportunity to ensure that his occlusion did not change with long-term use of the sleep apnea appliance.
Stage 3: Restorative Dentistry Completed
Once the occlusion is stable in Stage 2, it is possible to begin restorative treatment with any sextant. When the final restorations are placed, the sleep apnea appliance will need to be relined/refitted.
For this patient, restorations included:
• Provisionals to help verify that functional goals were met (Figure 12 through Figure 14 show this stage in more detail)
• Porcelain veneers on teeth Nos. 22 through 27
• Porcelain crowns on teeth Nos. 6 through 11 (Figure 15 and Figure 16); they were selected rather than veneers to have complete control over the lingual contour/envelope of function
• Monolithic IPS e.Max® (Ivoclar Vivadent, www.ivoclarvivadent.com) crown on tooth No. 19 (replacing a fractured porcelain-fused-to-metal restoration)
Digital Duplication
One of the most important steps in this process is the determination of the patient’s anterior guidance. During stage 2, the patient’s bite was adjusted through reductive and additive reshaping to create immediate separation of the posterior teeth (inside-out), and then, with the patient sitting up, the bite was adjusted in a postural position (outside-in). In this way, the anterior guidance was optimized to fill both requirements.
The final step is to make sure that in stage 3, the approved contours are duplicated in porcelain. One of the best ways to do this is to provide the laboratory with a model of these contours. This has typically been accomplished by taking impressions of a doctor-approved provisional restoration that the patient has had time to test. Otherwise, using digital technology, a model of the maxillary arch after the additive and reductive equilibration can be made from a scan, as was done in this case. The laboratory can scan the prep model with the provisional model and superimpose one over the other. It can then mill or print restorations that will precisely copy the contours that have been proven to work. For doctors doing chairside intraoral scanning, this can be done exactly the same way in fewer steps.
Conclusion
It would be much simpler for dentists if there were an either/or” to the “inside-out/outside-in ” debate. The “inside-out” camp could work out the entire occlusion on an articulator, creating steep contours to ensure posterior disclusion. The “outside-in” doctors could forget about posterior disclusion and simply make sure the anterior teeth don’t bump during chewing and speaking by tipping teeth forward or creating exaggerated concave lingual contours. Unfortunately, patients require both “inside-out” and “outside-in” functionality for a refined, lasting occlusion, and, as shown in the case presented, there is absolutely no reason to compromise by leaving something out.
Second to a stable, seated condylar position (CR), a correct anterior guidance is the single most important factor in an optimal occlusion—one that will be steep enough to disclude the posterior teeth in any excursive movement while being concave enough to be in harmony with the envelope of function. Building this into every anterior reconstruction will create beautiful restorations that will not only be comfortable, but also withstand the test of time.
About the Author
John C. Cranham, DDS
Private Practice
Chesapeake, Virginia
Clinical Director,
The Dawson Academy
References
1.Williamson EH, Lundquist DO. Anterior guidance: Its effects on electromyographic activity of the temporal and masseter muscles. J Prosthet Dent. 1983;49(6):816-823.
2. Davis CR. Maintaining immediate posterior disclusion on an occlusal splint for patient with severe bruxism habit. J Prosthet Dent. 1996;75(3):338-339.
3. Kerstein RB, Wright NR. Electromyographic and computer analyses of patients suffering from chronic myofascial pain-dysfunction syndrome: before and after treatment with immediate complete anterior guidance development. Cranio. 2006;24(3):156-165.
4. Kerstein RB. Reducing chronic masseter and temporalis muscular hyperactivity with computer-guided occlusal adjustments. Compend Contin Educ Dent. 2010;31(7): 530-534, 536, 538.
5. Gibbs CH, Lundeen HC. Jaw movements and forces during chewing and swallowing and their clinical significance. In: Advances in Occlusion. St. Louis, Mo: Mosby; 1982:2-32.
6. Bakeman EM, Kois J. The myth of anterior guidance. J Cosmetic Dent. 2012;28(3):57-62
7. Dawson PE. Evaluation, Diagnosis and Treatment of Occlusal Problems. 2nd ed. St. Louis, Mo: Mosby; 1989.
