An Introduction To Lip, Tooth, Ridge Classification

The prosthetic rehabilitation of the edentulous maxilla is known to be a challenge and requires meticulous planning. The complexity is mainly due to anatomical characteristics, bone resorption pattern, quality of bone, development of prosthetic emergence profile, oral hygiene limitations, influence of the teeth and hard tissue during speech and the important role the prosthesis plays in overall facial and dental esthetics.

This is why the LTR (Lip-Tooth-Ridge) classification was developed: to make navigating this rehabilitation planning smoother, swifter and, at the end of the day, more successful. Think of it as a guidepost for treatment planning the edentulous maxilla (either for fixed or removable prostheses) that helps clinicians identify the final prosthetic design while providing a case-specific risk assessment guide.

The LTR classification is based on the relationship between the optimal dimensions and position of the maxillary central incisor, the maxillary lip (dimensions and dynamics) and the architecture of the edentulous ridge.

Tooth Position

The maxillary incisal edge position is considered the starting point of any maxillary reconstruction. It is determined by analyzing dentofacial esthetics, tooth proportion, phonetics and the kinetics of the lower lip. This landmark position will be the keystone for developing the occlusal plane and vertical dimension of occlusion.

After proper positioning of the maxillary central incisor’s incisal edge, its inclination should be set following the facially generated treatment plan (Fig. 1).

During the smile design process, we should use the curvature of the lower lip as an anatomical reference to follow when determining the position of the maxillary teeth. The literature provides extensive clinical guidelines regarding the midline position, relationship between the upper lip and the zeniths of the maxillary teeth.

Lip

The upper lip position is one of the most important elements in anterior esthetics. Its static and dynamic assessment will play a crucial role in deciding the type of prosthetic design we will use for our patient.

In Tjan and Miller’s study, the smile for dentate patients was classified into high, medium or low based on the upper lip position, with medium and high corresponding to 80 percent of the population. In the circumstance of a medium smile, the maxillary lip moves apically to display the gingival levels of to the maxillary canines and incisors.

When it comes to the tools we use to capture these positions, our best bet is to go beyond basic photography. Recent studies have shown that the use of video in addition to photography has shown to be more effective in capturing the most apical position of the upper lip on maximum smile.

There are many huge benefits to using videos, not the least of which is the fact that they prove that a vast number of individuals are potentially at risk; a fact that is not so evident utilizing still photography.

Another important element related to facial esthetics is the determination of “adequate” maxillary lip support or lip projection. Lip projection at its apex is related to lip thickness, as well as support provided by the maxillary alveolar process and anterior teeth. However, “ideal” lip support is a range, and is thus completely subjective. In other words, our perception and assessment of this support are affected by many different factors.

Furthermore, the inclination of the maxillary incisors with respect to the frontal plane affects lip support. Our assessment of this parameter is what will guide our selection of a prosthetic design, including or excluding a labial extension also called "flange." This should be evaluated at rest and during function on a profile and frontal view as well as through comparison with a “flangeless design."

Ridge

Vertical and horizontal bone resorption of the residual alveolar ridge has been said to occur after complete extraction of the maxillary teeth. However, it is important to note that this resorption pattern has been described in complete denture patients over five to 25 years.

So if surgical procedures are conducted to preserve or augment the dimension of the ridge crest at time of extraction, and no removable complete denture is worn, the amount of alveolar ridge resorption can be expected to be significantly less.

The amount of post-extraction resorption will also be impacted by the alveolar bone level and status of the buccal plate around the teeth to be extracted. In other words, the fact that a patient presents with a maxillary removable complete denture does not necessarily imply that a labial prosthesis extension is mandatory.

By the same token, we cannot state that adequate prosthetic space is available to allow all types of prosthetic designs. It’s very important to understand that the lip support will be affected by the alveolar ridge resorption irrespective of its magnitude and loss of tooth structure.

Depending on the amount of bone resorption and the desired prosthetic design, the residual ridge geometry may need to be modified to ensure a convex emergence profile that will prevent food entrapment and promote appropriate oral hygiene procedures compatible with sustainable oral health.

As you can see, the main objective behind the LTR classification is to provide the interdisciplinary team with a graphic and comprehensive vision of the patient's condition. The LTR classification is divided in 4 classes (Fig. 2, 3, 4, 5).

Using this classification allows us to actually scrutinize the available prosthetic solutions and material rather than just having one prosthetic solution and trying to fit all patients into it.

Be on the lookout for part two, where we'll discuss the two fundamental processes associated with the LTR classification and what they mean for comprehensive patient evaluation.

(Click this link for more dentistry articles by Dr. Ricardo Mitrani.)

Ricardo Mitrani, D.D.S., M.S.D., Spear Faculty and Contributing Author

References:

• Zitzmann NU, Marinello CP. Fixed or removable implant-supported restorations in the edentulous maxilla: literature review. Pract Periodontics Aesthet Dent. 2000 Aug;12(6):599-608.
• Spear FM, Kokich VG, Mathews DP. Interdisciplinary management of anterior dental esthetics. J Am Dent Assoc. 2006 Feb;137(2):160-9.
• Rufenacht CR. Fundamentals of Esthetics. Berlin: Quintessence, 1990:67-134.
• Tjan AH, Miller GD, The JG. Some esthetic factors in a smile. J Prosthet Dent. 1984 Jan;51(1):24-8.
• Tallgren A. The reduction in face height of edentulous and partially edentulous subjects during long-term denture wear. A longitudinal roentgenographic cephalometric study. Acta Odontol Scand. 1966 Sep;24(2):195-239.