RME- Its effects on nasal tissues

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Maxillary expansion treatments have been used for more than a century to correct maxillary transverse deficiency. The most commonly used expansion treatment modalities are: rapid maxillary expansion (RME), slow maxillary expansion (SME) and surgically assisted maxillary expansion.

Rapid maxillary expansion (RME) is a common way to correct a narrow maxilla in adolescents by increasing the upper arch transverse dimensions mainly by separation of the two maxillary halves(orthopaedic effect) followed by buccal movement of posterior teeth and the supporting alveolar process(orthodontic effect). The main object of RME is to correct maxillary arch constriction but its effects are not limited to the maxilla as it is associated with 10 bones in the face and head. The skeletal effects for the maxillary hard tissue changes are well documented, but there are very few studies that examine RME effects on the nasal soft and hard tissue. In 2012, Study by Kim et al. was one of the first CBCT studies to evaluate nasal soft tissue changes. This was followed by Badreddine et al. in 2018, who studied changes in the noses of mouth-breathing patients using multislice computed tomography scans. These studies focused on the short-term nasal soft and hard tissue changes after expansion.

The article of our interest in the blog is the first study to compare the long-term effect of RME on nasal tissue with a non-treatment control group using CBCT.

Short-term and long-term effects of rapid maxillary expansion on the nasal soft and hard tissue: A cone beam computed tomography study

Cassie T. Truonga ; Hyeran H. Jeon ; Puttipong Sripinun ; Ann Tierney ; Normand S. Boucher

Angle Orthodontist 2021

What did this paper assess?

This study evaluated the short-term and long-term effects of RME on nasal soft and hard tissue and compare the effects with a control group using CBCT.

 

What was the protocol?

A retrospective study consisting of 63 patients.

Treatment group (TG) –

  • 35 patients (18 girls, 17 boys; average age 9.39±1.4)
  • with a constricted maxilla, treated with RME
  • A full coverage bonded rapid palatal expander extending from the maxillary primary or permanent canine to the maxillary first molar.

Activation protocol – Two turns per day (0.2 mm/turn) until adequate expansion was reached.

Control group (CG) –

  • 28 patients (16 girls, 12 boys; average age 8.81±1.6)
  • with skeletal Class 1 or mild to moderate Class 2 attributing to mandibular retrognathia with most patients having anterior arch perimeter deficiencies
  • Only subjected to routine records

 

CBCTs were taken at three time periods

  • T1 and T1’- As initial records of all 63 patients
  • T2 – Immediate post-RME (66 days) for the TG
  • T3 – 2.84 years after post-RME for the TG
  • T3’ – 2.25 years after T1’ for the CG

 

CBCTs were oriented in three planes of space.

  • Frontal- inferior rims of the orbit parallel to the floor.
  • Midsagittal- line was placed at the soft tissue of nasion, through the pronasale, to the middle of the chin.
  • Lateral -the FH line parallel to the floor. The coronal line was placed just posterior to the condyle.

The following landmarks- Alar width, Alar base width, Nasal length and height, Nasion-ANS height, ANS-PNS length, Pyriform height and width were measured in millimeters on the CBCTs in three dimensions in Dolphin Imaging (version 11.9; Dolphin Imaging & Management Solutions, Chatsworth, Calif).

 

 

What did their results show?

Immediate Post-RME Nasal Soft and Hard Tissue Changes

At the alar base width, there was a mean increase of 1.60 mm. For alar width, nasal length, and nasal height, there was an increase of 0.65 mm, 0.14 mm and 0.34 mm respectively. With the skeletal tissues, there was an increase of pyriform height of 1.77 mm and of pyriform width of 3.57 mm when comparing T1 and T2 of the TG. For nasion–anterior nasal spine (ANS) height and ANS–posterior nasal spine (PNS) length, there were increases of 1.04mm and 0.34 mm, respectively.

 

Long-Term Post-RME Nasal Soft and Hard Tissue Changes

 

Of 35 at T1, there were 22 at T2 and 25 at T3. Alar base width and pyriform height measurements that significantly increased immediately post-RME remained stable during a span of 2.58 years when compared with T3.There were increases in nasal height (+3.92 mm) and nasion–ANS height (+2.75 mm) and a decrease in pyriform width (-1.07mm), possibly attributed to vertical growth and skeletal transverse relapse during the follow-up period.

 

Long-Term Comparison of TG vs CG

 

The control group showed significant differences regarding all measurements except pyriform width from T1’ to T3’, demonstrating the effect of growth. The increase in pyriform width was 0.30 mm. There was no significant difference in the nasal soft and hard tissue measurements except for pyriform height and pyriform width attributed to the RME.

 

 

 

Critical appraisal

It is appreciable that this is the first study to compare the long-term effect of RME on nasal tissue with a non-treatment control group using CBCT. One of the first limitation is that, it is a retrospective study design. The authors intended to study the short and long term effects of RME on nasal soft and hard tissues and have successfully achieved it.

However some methodological constraints were noted, the control group patients revealed malocclusion but only records were taken initially with exposure to radiation and following the review of records, treatment was not initiated for 1 to 2 years. Also there was attrition in T2 and T3. Not all treatment groups had T1, T2, and T3 records and the possible reason for attrition mentioned in the study was that some patients required no additional treatment after palatal expansion but the quantification of maxillary constriction needs to be known to decide whether the treatment was actually not required?. The authors have not mentioned any data on the retention protocol post-RME treatment which plays a major role in post expansion stability. In addition, the power analysis was based on soft tissue changes after RME and not on the control group as the reference value for a control group was not found. However, the sample size was large enough to detect statistically significant findings.

 

 

Conclusion and scope for future studies:

This study suggest that, although RME produces some significant increase on the nasal soft tissue immediately after treatment, in the long-term this gain appears to be clinically similar to that observed in untreated control patients. The significant increase on the nasal hard tissue immediately after RME was maintained at long-term follow-up. There was a statistically significant difference in nasal hard tissue change between TG and CG at long-term follow-up attributed to the RME effect.

Future studies can be carried out with a prospective study design having two different age groups being treated with RME.

 

 

Contributors: Dr.M.Dilip kumar, Dr.Keerthi Venkatesan