Pre-surgical nasoalveolar molding for complete unilateral cleft lip and palate. Scoping review

DISCUSIÓN 

McNeil was the pioneer of the concept of an intraoral device designed to align cleft alveolar segments. However, it was Grayson who refined this idea by developing the presurgical nasoalveolar molding device (PNAM), an innovative device whose objective is not only to reshape the alveolar ridges but also to reshape the nasal cartilages, approaching a more functional and aesthetically normal anatomy. He also proposed that practitioners periodically modify the nasoalveolar molding plate at weekly intervals to progressively guide the segments toward their correct alignment.¹¹

However, nasoalveolar molding is a clinical technique that does not follow a standardized protocol, as shown in Table 5; consequently, the effects of nasoalveolar molding are conditioned by the specific protocols implemented in each case.10 During the first months of life, newborns exhibit plasticity and flexibility in their cartilage due to the high levels of estrogen and hyaluronic acid provided by the mother in the final stage of gestation. This principle is the basis for nasoalveolar molding. According to available statistical data, the nasal correction achieved through this method cannot be attained solely through surgery.^9,10

Table 6. Benefits and limitations of the use of the PNAM

Impact of PNAM Treatment

One of the main purposes of PNAM for patients with cleft lip and palate is to improve nasal symmetry, thereby enhancing the patient's aesthetics and social integration.^8,9 In the last decades, numerous studies have been conducted on the molding effects of PNAM. However, the results of these studies are variable.¹⁰

According to the evidence, a significant improvement in nasal symmetry has been found after PNAM therapy, with a significant increase in nostril height, nasal dome height, and columella length on the cleft side.⁹ This increase is attributed to the positive pressure actively exerted by the nasal stent against the nasal alae on the cleft side to help reshape the nose from its original flat form to a convex one, while also affecting the morphology of the non-cleft side.^8,9

Regarding the nasal stent, it is usually used once the cleft width has been reduced to 5 mm, in order to achieve soft tissue laxity and prevent an increase in nostril circumference. However, in the study by Titiz et al.,¹⁵ the possibility of introducing the nasal stent immediately was evaluated, achieving similar favorable results to those mentioned above, without the risk of causing a large nostril.

A significant decrease in the width of the nasal fossa and nasal dome was observed on the cleft side compared to the non-cleft side.^9,12 When comparing the conventional technique with its modified version, which is distinguished by the use of a 0.036 stainless steel wire in the former and a 0.032 titanium-molybdenum alloy in the latter, the results obtained were similar, showing an improvement in nasal morphology in both vertical and horizontal directions.^8,12

In addition, it has been documented that improved transmission of the force generated by the adhesive tape can promote greater verticalization of the columella compared to the classic method. Titiz et al.,¹⁵ compared their technique with Grayson's, where the tape is placed in an "L" shape, from the alar groove of the nose and the side of the non-cleft lip to the cheek on the cleft side, correcting the columella's axis within the limits allowed by the soft tissues.

In Grayson's technique, the applied force is absorbed primarily by the soft tissues of the non-cleft nasal fossa. However, in the modified technique presented by Titiz et al.,¹⁵ the modified nasal retainer in the non-cleft nasal fossa transmits the force generated by the tape and pushes the columella toward the midline, achieving a verticalization of 49.84°, greater than that obtained with the classic method.These results are consistent with the findings of Lautner et al.,¹⁰ who stated that the effectiveness of the NAM increases when the plate is properly supported on the palatal tissues and the labial segments are secured with tape through the cleft.

Another key objective of the NAM is the harmonization of the dental arch and the alveolar cleft region. A significant reduction in cleft space has been observed, leading to decreased lip tension.^8,10 These results were corroborated by Lautner et al.,¹⁰ and Dinh et al.,⁸ when comparing models using 3D measurements, as well as by Thakur et al.,⁸ when comparing the conventional Grayson technique with the modified one, demonstrating that proper alignment of the alveolar segments using non-surgical techniques provides a solid foundation for successful surgical lip closure.^8,10,12

Early orthopedic treatment in patients with cleft lip and palate (CLAP) results in changes on both the cleft and non-cleft sides of the maxilla. It has been observed that on the non-cleft side, the anteroposterior maxillary alveolar length decreases after intervention, compared to the total arch length.8 This phenomenon is also supported by the findings of Parhofer et al.,¹⁴ who compared the effects of the Passive Alveolar Modeler (PAM), a group that received the modified Hotz appliance, and the Naso-alveolar Modeler (NAM), as described by Grayson, on alveolar arch growth. Their findings indicated that patients treated with NAM experienced a significant reduction in anterior and medial maxillary width, while in the PAM group, these measurements remained stable. This change appears to be due to a greater mesial rotational effect of the major and minor alveolar segments, caused by the extraoral force of the adhesive tape, rather than anteroposterior maxillary growth. As a consequence, a midline shift of approximately two-thirds is observed, along with a reduction in the width of the anterior fissure.^8,14 Zheng et al.,¹¹ even observed a significant reduction in the inclination of the smaller segment when evaluating the coordinates in 3D programs, results that suggest that bone remodeling and rotation of the alveolar segments not only occur on the non-fissured side, but also on the fissured side, evidencing the impact of the treatment on both structures.¹¹

However, Ocak et al.,¹³ in their study indicates that there are no significant differences in maxillary arch measurements under NAM treatment in patients with cleft lip and palate (CLAP), regardless of its type (complete or incomplete). They also note that authors who document a reduction in cleft width, improved nasal symmetry, and decreased cleft severity in patients with unilateral CLAP may have found that these clefts form in the early stages of dental development, up to the first 6 months of life, with little follow-up over time.¹³ Furthermore, these authors point out that NAM therapy did not have a significant effect on the malocclusion characteristics observed, primarily because these patients had not yet reached peak mandibular growth, which could contribute to changes in conjunction with restricted maxillary growth and compression of the remaining scar.

Finally, Parhofer et al.,¹⁴ observed that in patients treated with PAM, the most significant changes occurred in sagittal measurements, accompanied by lateral rotation of the smaller alveolar segment. In contrast, with patients treated with NAM, the predominant effect was transverse compression of the maxilla. This suggests that the use of PAM could be more beneficial in cases of Class III malocclusion, severe maxillary compression, or mesial collapse of the smaller alveolar segment, as it allows for passive stimulation of growth in both directions.¹⁴ Furthermore, several studies have indicated that the correct positioning of the alveolar segments promotes the eruption of permanent teeth in optimal locations, which positively impacts long-term occlusal stability.^8,9

The scientific evidence analyzed supports the nasoalveolar molding technique as an effective, useful, passive, non-surgical, painless, and easily adaptable method that allows for redirecting the growth of soft and hard tissues, reducing cleft size, improving symmetry, facilitating surgery in the short term, and reducing the risk of scarring due to excessive retraction after surgery.^8,10-13

The scientific literature indicates significant advantages in the use of the nasoalveolar molding device (NAMD), including the possibility of facilitating future surgical intervention for nasal correction. Further-more, it is associated with simpler surgery and a reduced need for subsequent interventions such as bone grafts in later stages.^8,9 Thakur et al.,⁹ compared the conventional nasoalveolar molding technique with a modified PNAM technique, concluding that the latter is a favorable option due to several advantages: (1) it requires less office time; (2) it facilitates adjustments, and it reduces the need for subsequent nasal and dentoalveolar corrective procedures.³ According to Titiz et al.,¹⁵ the use of NAMs that are not directly attached to an intra-oral plate offers multiple advantages. These include allowing the patient to be fed with bottles specifically designed for infants with sucking difficulties and enabling continued use even if lesions or fungal infections occur that require a temporary interruption of treatment. However, in cases of severe clefts, it is recommended that the structure be complete, that is, that it includes its nasal stent, to achieve better control of the forces when aligning the segments.¹⁵

Parents play a vital role in the treatment, as they must be active participants for the success of nasoalveolar molding,10 especially when family members observe evident changes in the child within a short period, increasing their motivation. Additionally, the spaces created in the conformers allow for better airflow, reducing family anxiety by facilitating adequate breathing for the infant.¹⁵ Dinh et al.,⁸ Thakur et al.,⁹ and Lautner et al.,¹⁰ reaffirm the benefits in reducing the long-term psychological burden on the patient and their family. Further-more, they point out that it improves expectations regarding the treatment outcome and reduces the financial burden,^8-10 especially considering that in more severe cases, this treatment can be more complex and long-lasting, even into adulthood.¹⁴

Manufacturing Protocols and Digitization Processes

Part of the treatment includes adjustment sessions where the acrylic plate is polis-hed; however, this guideline is unclear, as it does not define specific areas for adding or removing resin, making the procedure highly dependent on the operator's experience. Therefore, it is not uncommon to observe unsatisfactory results after PNAM treatment, such as non-adherent alveolar processes or overlapping alveolar arches.¹¹

In this context, technological advances have led to improvements in the fabrication of the PNAM. Zheng et al.,¹¹ created a 3D coordinate system that allows for the objective description of changes in cleft palate segments, based on points defined by the author at the level of the tuberosity and the FH plane. Unlike common measurements, these coordinates represent not only the amount of molding but also the direction of this change. Because of this, dentists can modify the appliance according to the direction of change, activating and relieving pressure. In other words, they can guide dentists to improve the PNAM treatment procedure more precisely and efficiently. This has resulted in measurements and evaluations having a high interrater reliability coefficient, demonstrating better results in terms of reliability and sensitivity, as well as contributing to reduced laboratory time and eliminating the need for physical storage.^11-13 This innovative process has allowed for more precise alveolar modeling in each appliance, making the PNAM more efficient, optimizing processes, and reducing follow-up visits.

Side effects of NAM

The reviewed literature mentions mucosal ulceration and skin irritation as side effects of PNAM, especially on the cheeks. Therefore, the use of protective skin tape is recommended; the position should be changed at least once a week after it has completely dried. Applying dermal cream to reduce skin irritation and moisturize the exposed cheek is also recommended.⁸ In the treatment of patients with large cleft lip and palate, the choice of material for nasal stents is crucial. Titiz et al.,¹⁵ warn that orthodontic acrylic stents, even with a smoothed external surface, carry a high risk of nasal mucosal injury. This is because soft tissue tension in large clefts reduces the space available for stent insertion. To minimize complications in these cases, the exclusive use of soft acrylic is recommended. Soft acrylic stents with wings facilitate fixation to the face with adhesive tape, eliminating the need for support at the nasal base, unlike silicone stents, where soft tissue resistance requires anchoring to the floor of the nasal cavity. Furthermore, activation of retainers and tape adhesion are simpler with acrylic stents compared to silicone stents.¹⁵ Table 6 below summarizes the main benefits and side effects reported in the literature on the use of the nasoalveolar modeler.

Limitations of the studies

While this study provides valuable evidence on the potential effectiveness of the PNAM, its retrospective observational nature and the small number of studies limit the generalizability of the results. Larger and more heterogeneous randomized controlled clinical trials are needed to robustly validate the current findings, using standardized and/or clearly established protocols with long-term follow-up to assess the reliability of the results and the long-term benefits of the PNAM in patients with cleft lip and palate. Furthermore, the available evidence on the emerging techniques described in the reviewed literature is still preliminary. The scarcity of high-quality longitudinal and comparative studies prevents a rigorous evaluation of their efficacy and safety compared to established protocols.^10,12,13