Resting Position Lips at Rest and Tooth Appearance

The esthetic evaluation and treatment planning for anterior dentition restorations must consider not only the appearance of teeth during smiling and functional activities, but also the tooth display characteristics present at rest, when the lips are in their natural relaxed position. The resting lip position, determined by a complex interplay of skeletal anatomy, neuromuscular control of facial and oral musculature, and lip morphology, fundamentally influences the proportion of anterior teeth visible in social and professional interactions. Understanding the relationship between lip position at rest and tooth display characteristics enables clinicians to develop treatment plans that optimize esthetic outcomes across all functional states and to develop realistic patient expectations regarding the visible results of restorative procedures.

Lip Anatomy and Kinematics at Rest

The human lip represents a complex anatomic structure comprising multiple muscle layers, including the orbicularis oris muscle (the principal sphincter muscle of the lips), buccinator muscle, levator labii superioris, zygomaticus major and minor muscles, depressor anguli oris, and multiple other smaller muscles that collectively control lip position and movement. At rest, with the patient in a relaxed, upright posture, the lips assume a position determined by the resting tone of these musculature groups, the degree of skeletal overbite, and the morphology (length and thickness) of the lips.

The vertical position of the maxillary lip at rest is primarily determined by the resting tone of the levator labii superioris muscle and the elasticity of the upper lip tissue. In individuals with normal skeletal relationships and adequate lip length, the maxillary lip overlaps the maxillary central incisor by approximately 2-4 millimeters, with the lip margin positioned at or slightly below the gingival margin of the maxillary anterior teeth. The mandibular lip position is determined by the resting tone of muscles controlling mandibular position and the amount of anterior overbite, typically covering the incisal 2-4 millimeters of maxillary central incisors and the incisal third of maxillary lateral incisors.

Variations in lip length, thickness, and tonicity create substantial individual variation in the amount of tooth display at rest. Individuals with short upper lips (measuring less than 20 millimeters from the nasal base to the lip margin) demonstrate greater maxillary anterior tooth display at rest, often showing 10-15 millimeters of central incisor clinical crown. Conversely, individuals with long upper lips (exceeding 25 millimeters) may demonstrate minimal anterior tooth display at rest, with only 2-3 millimeters of incisor crowns visible. These individual variations in lip morphology must be acknowledged during treatment planning to ensure that treatment objectives align with the patient's existing lip characteristics.

Tooth Display Characteristics at Rest

The proportion of anterior dentition visible at rest, and the relationship between tooth crowns and gingival contours, constitutes a critical component of esthetic assessment and treatment planning. In individuals with normal maxillofacial proportions, the maxillary lip at rest typically overlaps the maxillary central incisors by 2-4 millimeters, exposing approximately the incisal third to two-thirds of the central incisor crowns. The lateral incisors are typically displayed less extensively, with the lip covering approximately 50-75% of the clinical crown. Canines are often nearly completely covered by the relaxed lip, with only the incisal tip visible in many individuals.

The gingival display at rest should be minimal, with the maxillary lip positioned at or slightly below the gingival margins of the anterior teeth. Individuals demonstrating gingival display of greater than 2-3 millimeters at rest are considered to display a "gummy smile," a term descriptive of the esthetic concern associated with excessive gingival visibility. The presence of gingival display at rest may be attributable to skeletal factors (excessive maxillary anterior-posterior height or vertical maxillary excess), neuromuscular factors (hyperactivity of the levator labii superioris muscle), or dental factors (excessive dentoalveolar height or vertical relationships).

The mandibular lip position at rest and the degree of anterior tooth display are determined by the skeletal and dental relationships of the mandible relative to the maxilla. Individuals with normal Class I skeletal and dental relationships typically demonstrate minimal display of mandibular anterior teeth at rest, with the mandibular lip positioned to cover the incisal 2-4 millimeters of maxillary central incisors. Individuals with skeletal or dental Class II relationships (maxillary prognathism or maxillary dentoalveolar protrusion relative to the mandible) demonstrate greater maxillary tooth display and may demonstrate some mandibular incisor display. Conversely, individuals with skeletal or dental Class III relationships (mandibular prognathism) typically demonstrate reduced maxillary tooth display and greater mandibular tooth display.

The aging process produces progressive changes in lip morphology and positioning that substantially influence tooth display at rest. As individuals age, vertical facial dimensions progressively decrease due to alveolar bone resorption, tooth wear, and loss of facial support. These morphologic changes are accompanied by progressive loss of lip elasticity, sagging of tissues due to gravity, and thinning of lip tissue, all of which contribute to altered lip positioning during rest.

In older individuals, the maxillary lip often assumes a lower position due to progressive loss of elasticity and increased coverage of the maxillary anterior teeth. Paradoxically, while the lip covers more of the maxillary incisor crowns, the teeth themselves appear smaller and shorter due to both actual shortening from wear and the visual effect of increased gingival display during function (smiling). The mandibular lip positioning often becomes lower as well, and in some older individuals, the mandibular lip may rest below the incisal edge of the maxillary central incisors, creating a more pronounced anterior overbite appearance.

The transition from youthful to aged lip positioning typically occurs gradually over many decades, but the rate of change may accelerate significantly following dental procedures that alter vertical dimension of occlusion or when significant tooth loss occurs. Patients undergoing extensive anterior restorations should be counseled regarding age-appropriate tooth display expectations, and treatment objectives should be modified to match the patient's age and existing lip morphology rather than attempting to create a youthful appearance in an older patient with naturally aged lips and skeletal proportions.

Treatment Planning Considerations for Resting Lip Position

Esthetic treatment planning for anterior dentition restorations must incorporate systematic assessment of resting lip position and tooth display, as these characteristics fundamentally influence the clinical success and patient satisfaction with restorative outcomes. Patients should be asked to assume a relaxed posture and to allow their lips to rest in their natural position without conscious effort to maximize or minimize tooth display. Digital photography of the patient in this relaxed state, with the lips at rest, provides an objective reference for tooth display assessment and enables documentation of pre-treatment tooth display for comparison with post-treatment results.

The amount of anterior tooth display at rest should be assessed and documented, noting the relationship between the maxillary lip margin and the gingival margin of the anterior teeth. The visibility of the anterior teeth at rest should be quantified in millimeters of clinical crown exposure, and this dimension should be compared with age and ethnicity-appropriate norms. For patients demonstrating excessive or insufficient tooth display at rest, the clinician should determine whether the discrepancy results from lip morphology (short or long upper lip, hypertonic or hypotonic muscles), skeletal factors (vertical maxillary excess or deficiency), or dental factors (excessive or insufficient dental show).

When anterior restorations are required, the clinician should strive to maintain the existing tooth display at rest unless specific esthetic concerns warrant modification. If the patient presents with a "low smile line" (minimal display of maxillary anterior teeth during smiling), minor dental esthetic corrections are often satisfactory because limited tooth visibility during social interactions reduces the visual impact of any esthetic imperfections. Conversely, patients with a "high smile line" (extensive display of maxillary anterior and gingival tissues during smiling) require meticulous attention to every detail of anterior tooth and gingival esthetics because these structures will be extensively visible during their most frequent interactions.

Gummy Smile Considerations and Management

The term "gummy smile" describes the excessive display of gingival tissues visible during smiling. The clinical significance of gummy smiles varies substantially among cultures and individuals, with some patients considering them a significant esthetic concern warranting treatment, while others minimize their importance. Gummy smiles become relevant to anterior restorative treatment planning when (1) the patient identifies excessive gingival display as an esthetic concern, (2) the restorative procedure will alter vertical dental relationships and potentially affect gingival display, or (3) gingivectomy or esthetic crown lengthening procedures are being considered as part of comprehensive esthetic rehabilitation.

The etiology of gummy smiles must be systematically evaluated to determine the most appropriate treatment approach. Skeletal causes of gummy smile, such as vertical maxillary excess (excessive anterior-posterior height of the maxilla relative to the mandible), require orthognathic surgical correction for definitive management and should not be addressed through dental treatment modalities. Dental causes of gummy smile, including excessive dentoalveolar height (teeth that erupt excessively into the alveolar bone creating excessive alveolar bone), may be managed through surgical crown lengthening or gingivectomy procedures that reposition the gingival margin apically to reduce gingival display.

Neuromuscular causes of gummy smile, including hyperactivity of the levator labii superioris muscle, are difficult to address through prosthodontic treatment but may respond to injection of botulinum toxin (Botox) which temporarily paralyzes the hyperactive muscle. For patients undergoing anterior restorations who present with gummy smile, the clinician should counsel regarding the limitations of prosthodontic treatment in addressing skeletal or neuromuscular causes and should recommend appropriate specialist consultation (orthodontist, periodontist, or oral and maxillofacial surgeon) if the patient desires definitive management.

Vertical Dimension and Lip Support Considerations

The vertical dimension of occlusion (VDO), defined as the vertical relationship between the maxilla and mandible during closed mouth position with the teeth in static occlusion, fundamentally influences the apparent length of anterior tooth crowns visible at rest and the degree of lip support provided by the anterior teeth. In individuals with normal VDO and normal anterior overbite, the anterior teeth provide optimal support to the lips, creating balanced facial proportions and appropriate tooth display.

Restorative procedures that alter VDO, such as replacement of worn anterior teeth with restorations of increased clinical crown length, may alter the appearance of tooth display at rest and may affect lip support and facial esthetics. When replacing worn anterior teeth, the clinician should restore VDO to levels consistent with the patient's age-appropriate facial dimensions while ensuring that the restoration provides adequate lip support to prevent a sunken or aged appearance. However, in patients with limited anterior tooth display at rest (due to long upper lips or neuromuscular factors), restoration of normal VDO may result in minimal visible change in tooth display at rest.

Conversely, restorative procedures that decrease VDO, such as extraction of anterior teeth followed by denture construction without maintenance of original VDO, may result in reduced lip support, loss of facial height, and an aged appearance. This principle emphasizes the importance of careful VDO assessment and meticulous attention to vertical relationships during anterior restorative procedures, particularly in patients requiring comprehensive anterior rehabilitation.

Assessment and Communication with Patients

Effective communication with patients regarding resting lip position and tooth display characteristics is essential to develop realistic treatment expectations and to ensure patient satisfaction with restorative outcomes. During the consultation and treatment planning phase, the clinician should explain the relationship between the patient's existing lip morphology and tooth display characteristics, demonstrating through clinical photographs or drawings how the existing lips influence tooth visibility.

For patients whose resting lip position results in minimal anterior tooth display, the clinician should counsel that subtle dental esthetic corrections may have limited visibility in social contexts where tooth display is minimal. For patients with prominent lip display, the clinician should emphasize the importance of meticulous esthetic refinement during restorative procedures because their anterior teeth will be extensively visible during daily interactions.

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Understanding the relationship between resting lip position, tooth display characteristics, and patient-specific factors enables clinicians to develop comprehensive esthetic treatment plans that produce results satisfying to patients and aligned with their individual anatomic characteristics and esthetic values. Recognition of these relationships transforms the esthetic evaluation from a simple assessment of tooth color and form to a comprehensive analysis of the dentofacial complex that considers individual variation and patient-specific factors.