The results of this investigation appear to indicate that with a patient in natural head position, the ideal inclination of a tangent to the labial face of the maxillary incisor crowns in profile view will be approximately parallel to the true vertical line and thereby approximately perpendicular to the true horizontal line. The most attractive inclination was the 85° retroclined position, with a range of 80 to 95° being acceptable in terms of observer acceptance. Overall, excessive proclination appears to be less desirable than retroclination, and beyond 105° most observers recommend treatment.
Cao et al.  and Chirivella et al.  evaluated profile smile attractiveness in relation to maxillary incisor inclination and sagittal position. Both groups of investigators used the Andrews’ method of assessing maxillary incisor position in relation to the inclination of the forehead , which is a questionable concept in relation to why the forehead inclination should be aesthetically relevant to incisor position, particularly considering the wide variation in forehead inclination within any ethnic population . Nevertheless, Cao et al.  found that the most attractive image had a “5° lingual inclination,” which is approximately equivalent to the 85° inclination found in this investigation. Chirivella et al.  appear to suggest that the degree of proclination or retroclination depends on the facial type, with dolichocephalic facial patterns having maxillary incisor inclinations of 15° proclination or retroclination as the most attractive images. These results are not verified by the current investigation.
Giron de Velasco et al.  assessed the influence of “maxillary incisor torque,” by which they appear to mean incisor inclination in relation to the functional occlusal plane, on the aesthetic perception of the smile. Their online survey assessed three groups, and they found that laypeople preferred the 80° inclination, specialists in dental aesthetics preferred the 75° inclination, and the orthodontist group preferred the 70° inclination. Although the angles are not directly comparable as the authors were using different measuring parameters, nevertheless their results were significantly at variance with those of this investigation.
There are a number of practical implications for the results of this investigation. Orthodontists routinely alter the inclination of the maxillary incisors, and any major restoration of the maxillary anterior segment, from crowns and bridges to dental implants, must consider the inclination of the maxillary incisor crown face. The planned position of the maxillary incisor should be based on the position providing the best aesthetic result, i.e. the inclination of the labial face of the maxillary central incisor crowns in relation to the face, rather than on cephalometric values relating the entire long axis of the teeth to any anatomical reference plane. Additionally, treatment for orthognathic surgery patients with a significant anterior open bite often entails a differential posterior impaction of the maxilla, i.e. the posterior maxilla is elevated more than the anterior maxilla, with the maxilla rotating clockwise around the transverse axis, allowing the mandible to autorotate forward. Associated with such differential maxillary impaction, the maxillary incisors will retrocline, and, as such, a compensatory degree of incisor proclination must be built into the preoperative orthodontic preparation . Additionally, if a segmental maxillary procedure is undertaken, rotation of the anterior segment containing the four incisor teeth will also change the inclination of the incisors . In all these situations, the final inclination of the maxillary incisor crowns should be planned.
A purely anecdotal observation is the presence of a very mild Class II division 2 malocclusion, and thereby very mildly retroclined maxillary incisors, is rather common in attractive professional models and actors. Any relevance to the results of this investigation remains purely speculative.