Importance of Capturing the Midline and Horizontal Line Angles of a Patient’s Face and the Importance of the Communication of This Record from Dentist to Laboratory
The main objective of dental aesthetics treatment is to restore an otherwise damaged dentition to its natural, healthy appearance. Aesthetics, on the other hand, means naturalness, beauty, and a youthful appearance about one’s age. Rifkin and McLaren call dental aesthetics the “art of the imperceptible”. A lovely dental appearance is the subjective appreciation of the shape, shade and arrangement of the teeth in relation to the lips, gingival and other facial features. Symmetry, the property of being balanced, with correspondence in shape, size, and relative position of parts of the teeth on opposite sides of a dividing line or about a centre or median plane or axis, play the largest part in the perception of dental rehabilitation.
According to a study by Dunn when he was evaluating different photographs of male and female smiles, out of the 25 demographic groups, 24 picked the same attractive female smile and natural teeth characterized this smile, which was having a high lip line, a light shade, and a large display of teeth and radiating symmetry. In addition, several other studies proved that society has a greater impact on appearance. This shows that attractive people have a higher probability of being more successful and getting higher paying and jobs that are more prestigious, better luck in obtaining dates, positive responses, and more favorable jury verdicts even from infants. However, the ability of a dentist to communicate the midline and horizontal line angles of the patient’s face to the dental technician in the laboratory will state the success of the dental aesthetic outcome.
The Dental Midline
The median plane is the line that passes through the middle of the body longitudinally from front to back thereby dividing it into the right and left equal halves. The facial midline is a vital reference position used for determining multiple design criteria in relation to the maxillary midline position. It is also relative to the facial midline used in orthodontic treatment planning. It is also the main functional component of occlusion. According to Miller, the location of the midline is exactly in the middle of the mouth in approximately 70 per cent of people. He also confirmed that mandibular and maxillary midlines fail to coincide in more than three-fourths of the world population. The mandibular midline deviation from the facial midline is the most common asymmetry trait. Thus, when deciding where to put the maxillary midline, the dental technician does not make use of the mandibular midline as a reference point.
The Incisal Horizontal Line Angles
The reference plane that is used to determine the incisal horizontal plane is the interpupillary line, which leads to the occlusal plane and the gingival plane. When an incisal plane cant is 1mm, it is rated as significantly less aesthetic. According to Kockich, an occlusal plane cant is a very distressing smile characteristic to laypeople and health professionals. Also, an incisal occlusal cant is a form of irregularity that is obvious when a person smiles but is not perceived on study casts or intraoral images. The condylar determinants do not make use of the aesthetic orientation requirements even when using a face-bow transfer. This is because we evaluate and transfer the posterior and anterior occlusal determinants from a functional standpoint to the articulator with the hypothesis that the dental aesthetic orientation of the anterior teeth is correct. Also, the position of these teeth may not represent the incisal horizontal line angles of the incisors when referring to the remaining unprepared teeth.
Midline Cant or Oblique Midline
Ideally, the midline of the teeth should be completely vertical and be centered in the face. However, it is important to ensure that the anterior teeth are oriented vertically in the face and perpendicular to the incisal plane even if the midlines of one or both curves are not centered. As axial midline angulation increases, acceptability ratings and attractiveness scores decline consistentl6. According to several studies, it has been shown that midline deviations (between 3 mm or 4 mm) are not noticed by many people especially if the long axis of the face is parallel to the long axes of the teeth. According to Spear, the mediolateral inclination of the maxillary incisors is the most important relationship to evaluate. If the incisors are inclined by 2 mm to either left or right, people regard this as unaesthetic. Thus, this type of midline deviation (or the oblique midline) is visible, and dentists should use interproximal preparation to correct this.
After the dental restoration, the dentist will have to transfer these important parameters of the midline and the incisal horizontal line angles of the patient’s face to the dental technician. All these parameters will be referenced to the interpupillary line and facial midline, but how is this reliably accomplished?
Back in the days, cotton swabs, pencils, classic stick bites and symmetry bites were used to capture these dimensional relationships. However, this method was discarded due to its unlimited limitations. These limitations are mainly due to the short working time available with many bite registration materials; this means that the technician will have to work quickly to center and place these results before the material sets. The dentist and the technician will have to repeat the whole process if the symmetry bite or stick bite is slightly off. With fixed symmetry bites, the horizontal and vertical are fixed at exactly 90 degrees to each other, assuming the interpupillary line matches exactly to the horizontal incisal plane and they do not anticipate or indicate any correction. Also, a stick bites to the horizontal means that the patient can keep his or her head absolutely still and upright.
Onebite™, which means Precision Dental Products; Draper, Utah, is a facial plane relator and is the only available simple solution that makes the transfer of the required data from the dentist to the dental technician. This is the best because it has some distinct advantages over other available systems. One of which is that it eliminates the repetition of the procedure when the bite fork is placed slightly off-centre; this is made possible because the bite fork portion is separated from the adjustable horizontal and vertical components.
Another reason why Onebite is better than others is that the technician can lock and leave the horizontal and vertical components in a locked 90-degree relationship if the patient shows symmetry of the horizontal, midline and interpupillary line. Also, the technician can unlock the components by rotating the horizontal bar; this way, the locking pins will be facing the technician, if there is a divergence with the interpupillary line. In addition to this, the components of the Onebite can be taken apart by forcing the locking screw laterally; this facilitates transport to the laboratory. This shows another advantage of Onebite; that is its length can be reduced at the plastic cross supports. This will make it fit onto a semi-adjustable articulator easily.
The validation for the need of accurate communication by the dental clinician to the laboratory technician of the incisal midline cant, incisal horizontal plane and the dental midline and have been discussed. The importance of the communication of this record needs a simple technique that facilitates this communication. This technique should minimize the need for exclusive remakes for aesthetically driven restorations and dental rehabilitation.