Profile esthetics is generally becoming one of the major objectives of patients seeking orthodontic or orthognathic therapies nowadays. The lip is the pivotal feature affecting the esthetics of the lower third of face, especially as upper lip attracts the greatest attention.

The main function of the lips, ie, oral competence, is controlled by Orbicularis oris muscle¹ and the mentalis muscle. In cases like  bimaxillary protrusion or severe class II div 1, lip incompetence often results in  hypertrophic muscle activity as subjects unconsciously exert effort to keep their lips closed at rest. Apart from this muscle activity, Profit found that the resting lips also have a possible influence on the dentition². Tomes almost 100 years ago advanced a theory that it is the perioral musculature and lips and tongue that principally determine the position of teeth¹. The balance of these muscles is very important in the growth and development of craniofacial region and also credited in post treatment retention and stability. So, as an Orthodontist, it is important to measure the perioral muscle force but since pressure measurement is more difficult than strength, so force or strength measurement is preferable.

It is hypothesized that this perioral muscle force will vary between different malocclusions. So, various studies have been conducted to relate the effect of lip force on craniofacial growth  but with conflicting results.

Posen conducted a study to measure the strength of lips in subjects with Angle Class II div 2 and subjects with bimaxillary protrusion and found that the subjects with class II divison 2 had high lip strength and subjects with bimaxillary protrusion had low lip strength³.

Ingervall and Theur  investigated the relationship between lip strength, bite and facial morphology and concluded that lip strength was small in children  with  large overjet , long dental arches, proclined incisors or Angle Class II malocclusion and children with large interlabial gap⁴.

Ingervall and Janson Profit et al⁵ concluded that subjects with hypodivergent growth pattern have greater development of their perioral and masticatory musculature than the hyperdivergent growth pattern but Jung¹ and Hodge et al found no significant correlation between horizontal skeletal pattern and the upper lip closing force in their studies¹.

Lambrechts et al⁶ investigated  any difference in lip pressure on the basis of gender, Angle classification and characteristics of malocclusion and concluded that lip pressure was higher in males subjects than females  and higher  lip pressure in  class I malocclusion than class II div 1 malocclusion subjects.

Due to controversial results and none of the study on class III malocclusion, the research in various craniofacial patterns remains unclear.

Many methods have been introduced to measure force or pressure put by lips in oral cavity like Pommeter consisting of a mouthpiece connected to a dynamometer, Electomyography , Y-meter  ,  force sensing resistor device ( flexiforce low type) ,  Myometer160, bulb filled with some fluid and Oral Performance Instrument . However ,they all have one or the other drawbacks like the flexiform sensors are too costly and fragile and also produce errors when used for long time.The dynamometers are less sensitive.IOPI is also not affordable.The air filled bulbs have problem in positioning and reproductiblity within oral cavity.

So, in this,  study a MD30-60 SENSOR will be used to measure the vertical vector of lip closing force. It is cost effective, simple and easy to integrate, ultra thin, durable and delivers stable performance over time, waterproof, pressure sensitive for versatile applications.

To the best of my knowledge,none of the study has evaluated lip  force in various skeletal malocclusions with different growth patterns. So, the aim of this  study is to evaluate and compare lip closing strength in various skeletal malocclusions with different growth patterns in males and females and lip strength at rest and during swallowing.