Significance of saddle angle in myofunctional therapy: A case series

Introduction

Class II malocclusion is one of the most common problem around the globe affecting about one third of the patients seeking orthodontic treatment. McNamara stated that a retrusive mandible is the most common feature of this malocclusion. ^[1] Functional appliances can be used to correct both skeletal and dental problems in these patients. These appliances have been used since the 1930s. despite their long history, there is still much controversy surrounding their use, mode of action, and effectiveness. Twin block appliance therapy is more effective at correcting class II malocclusion through skeletal changes than most other appliances, making it suitable for early orthodontic treatment in patients with class II malocclusion. ^[2] Myofunctional therapy is not a universal treatment approach for all growing patients, and several factors must be considered when choosing the best course of care. Saddle angle is one of the most crucial factors in the success of myofunctional treatment.

Saddle angle: Saddle angle, a concept introduced by Rakosi, is the angle between the anterior and posterior cranial bases.^[3] (N-S-Ar; nasion-sella- articulare) as shown in [Figure 1].

A large saddle angle indicates a posterior position of the fossa and a small saddle angle indicates an anteriorly positioned fossa.

Graber, Rakosi, and Petrovic suggested that a large saddle angle often indicates a posteriorly displaced condyle and mandible relative to the cranial base and maxilla. This is unless the fossa position is compensated for specific angular (articular angle) and linear (ramal length) relationships. Notably, a non-compensated posterior mandibular position due to a large saddle angle is highly resistant to correction through functional appliance therapy. ^[4]

There are three case reports in this study that describe growing patients treated with a twin block appliance to correct skeletal class II malocclusion. All parameters were favorable for myofunctional therapy, except for the increased saddle angle. These cases demonstrate the impact of saddle angle (N-S-Ar) on the effectiveness of myofunctional treatment.

Case Report 1

12 years old prepubertal male diagnosed with class II skeletal base, orthognathic maxilla, retrognathic mandible, straight path of closure. He had Angle’s class II malocclusion: increased inclination of maxillary anteriors and retroclined mandibular incisors, increased overjet and overbite, deep curve of the spee. The upper and lower midlines did not coincide. Patient’s profile was convex, with an obtuse nasolabial angle ([Figure 1], [Figure 2]). The cephalometric measurements are mentioned in [Table 1].

Growth prediction

(i) CVMI 2 (acceleration stage): 65 – 85% growth remaining ([Figure 4])

The treatment plan was divided into two phases:

Phase I

Functional therapy with the Twin Block appliance

Phase II

Fixed mechanotherapy

      

Phase I

Functional therapy with the Twin Block appliance

The patient was treated with twin block appliance, to bring mandible forward till a class I skeletal base was achieved. Phase 1 therapy was completed in 9 months.

I. Objectives achieved after phase I ([Figure 8], [Figure 9])

Class I skeletal base

Class I molar relation

Class I canine relation

Normal overjet and overbite

   

Phase II

Fixed mechanotherapy

After the first phase was completed, the second phase began with fixed mechanotherapy in a pre- adjusted edgewise MBT.022-inch slot. Initially, 0.016 Heat Activated Nickel Titanium wire was used for levelling and alignment.

Treatment outcome

After two months of completion of phase 2 (levelling and alignment), it was found out that the treatment had undergone relapse. ([Figure 12], [Figure 15])

Cranial base to point A angle was the same, cranial base to point B angle had decreased due to retropositioned mandible (ANB = 8⁰) resulted in increased overjet.

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Measurements	Normal	Pretreatment	After completion of Phase 1	After levelling and alignment of lower arch
SNA	82⁰ ± 2⁰	80⁰	81⁰	81⁰
SNB	80⁰ ± 2⁰	73⁰	77⁰	73⁰
ANB	2⁰	7⁰	4⁰	8⁰
Beta angle	27⁰ - 35⁰	22⁰	23⁰	21⁰
Yen angle	117⁰-123⁰	113⁰	118⁰	115⁰
Pie angle	1.3⁰-5⁰	1⁰	2⁰	1⁰
W angle	51⁰ - 56⁰	45⁰	50⁰	46⁰
N perpendicular to point A	0±2mm	0mm	1mm	1mm
N perpendicular to point – pog	0 - -4mm	-9 mm	-6mm	-9mm
Saddle angle	123⁰±5⁰	131⁰	130⁰	131⁰
Articular angle	143⁰±6⁰	141⁰	139⁰	141⁰
Gonial angle	128⁰ ± 7⁰	122⁰	123⁰	122⁰
Effective mandibular length	120 ± 3.4mm	96mm	97mm	97mm
Effective maxillary length	92.1 ± 2.7mm	81mm	83mm	83mm
Witts appraisal	0-2 mm	4mm	1mm	4mm
Upper   incisor   to NA	22⁰/4mm	39⁰/7mm	40⁰/7mm	40⁰/7mm
Lower   incisor   to NB	25⁰/4mm	24⁰/2mm	26⁰/2mm	27⁰/5mm
IMPA	90⁰	93⁰	95⁰	98⁰
Interincisal angle	131⁰	121⁰	119⁰	118⁰
Y axis	66⁰	58⁰	62⁰	61⁰
Upper lip to S line	0mm	2mm	0mm	2mm
Lower lip to S line	0mm	-1mm	0mm	-1mm
Nasolabial angle	90⁰-110⁰	118⁰	121⁰	123⁰
Intercanine width		U- 33mm L- 26mm	U- 33mm L- 26mm	U- 33mm L- 26mm
Intermolar width		U- 42mm L- 37mm	U- 42mm L- 37mm	U- 42mm L- 37mm

Table 1 Comprehensive cephalometric evaluation

Case Report 2

13 years old prepubertal female diagnosed with class II skeletal base, orthognathic maxilla, retrognathic mandible, straight path of closure with Angle’s class II malocclusion: increased inclination of maxillary anteriors and retroclined mandibular incisors, increased overjet and overbite. Patient’s profile was convex, with an obtuse nasolabial angle. ([Figure 17]) The cephalometric measurements are mentioned in [Table 2].

Problem list

Skeletal problem

Class II skeletal base

Retrognathic mandible

Average growth pattern

Dental problem ([Figure 18])

End on molar relation and end on canine relation on both sides

Increased inclination of the maxillary anteriors

Retroclined mandibular incisors

Increased overjet and overbite

Forwardly placed upper incisors

Soft tissue problems

Convex profile

Obtuse nasolabial angle

Retruded lower lip

Protrusive upper lip

Measurements	Normal	Pretreatment	After completion of myofunctional therapy
SNA	82⁰ ± 2⁰	80 ⁰	81⁰
SNB	80⁰ ± 2⁰	74⁰	74⁰
ANB	2⁰	6⁰	7⁰
Beta angle	27⁰-35⁰	25⁰	23⁰
Yen angle	117⁰-123⁰	115⁰	118⁰
Pie angle	1.3⁰ -5⁰	1⁰	2⁰
W angle	51⁰-56⁰	49⁰	50⁰
N perpendicular to point A	0 ± 2mm	0 mm	1mm
N perpendicular to point – pog	0 - -4mm	-9 mm	-6mm
Saddle angle	123⁰±5⁰	134⁰	134⁰
Articular angle	143⁰±6⁰	139⁰	139⁰
Gonial angle	128⁰±7⁰	122⁰	123⁰
Effective mandibular length	120±3.4mm	93mm	94mm
Effective maxillary length	92.1±2.7mm	81mm	82mm
Witts appraisal	0-2 mm	4mm	1mm
Upper   incisor   to NA	22⁰/4mm	39⁰/7mm	40⁰/7mm
Lower   incisor   to NB	25⁰/4mm	24⁰/2mm	25⁰/2mm
IMPA	90⁰	95⁰	95⁰
Interincisal angle	131⁰	118⁰	119⁰
Y axis	66⁰	64⁰	65⁰
Upper lip to S line	0mm	2mm	0mm
Lower lip to S line	0mm	-1mm	0mm
Nasolabial angle	90⁰-110⁰	113⁰	114⁰
Intercanine width		U- 30mm L- 27mm	U- 30mm L- 27mm
Intermolar width		U- 43mm L- 39mm	U- 43mm L- 39mm

Table 2 Comprehensive cephalometric evaluation

Treatment outcome

Twin block treatment was done for 9 months ([Figure 20]), and monthly follow up was done. There were no positive response to the treatment obtained. ([Figure 21], [Figure 22])

Case Report 3

12 years old prepubertal male diagnosed with class II skeletal base, orthognathic maxilla, retrognathic mandible, straight path of closure with Angle’s class II malocclusion: increased inclination of maxillary anteriors and proclined mandibular incisors, increased overjet. Patient’s profile was convex, with an obtuse nasolabial angle (due to upturned nose). ([Figure 27]) The cephalometric measurements are mentioned in [Table 3].

Problem list

Skeletal problem

Class II skeletal base

Retrognathic mandible

Dental problem ([Figure 28])

Angle’s class II molar relation and end on canine relation on both sides

Increased inclination of the maxillary anteriors

Retroclined mandibular incisors

Increased overjet

Forwardly placed upper incisors

Spacing in upper and lower arch

Soft tissue problems

Convex profile

Obtuse nasolabial angle

Potentially incompetent lips

Retruded lower lip

Protrusive upper lip

 

Measurements	Normal	Pre-treatment	After completion of myofunctional therapy
SNA	82⁰ ± 2⁰	81⁰	81⁰
SNB	80⁰ ± 2⁰	74⁰	74⁰
ANB	2⁰	7⁰	7⁰
Beta angle	27⁰-35⁰	22⁰	23⁰
Yen angle	117⁰-123⁰	113⁰	118⁰
Pie angle	1.3⁰-5⁰	1⁰	2⁰
W angle	51⁰-56⁰	45⁰	50⁰
N perpendicular to point A	0±2mm	0mm	1mm
N perpendicular to point – pog	0 - -4mm	-9 mm	-6mm
Saddle angle	123⁰±5⁰	135⁰	135⁰
Articular angle	143⁰±6⁰	138⁰	138⁰
Gonial angle	128⁰±7⁰	123⁰	124⁰
Effective mandibular length	120±3.4mm	96mm	97mm
Effective maxillary length	92.1±2.7mm	81mm	83mm
Witt’s appraisal	0-2 mm	4mm	1mm
Upper incisor to NA	22⁰/4mm	42⁰/7mm	44⁰/7mm
Lower incisor to NB	25⁰/4mm	23⁰/2mm	25⁰/2mm
IMPA	90⁰	96⁰	96⁰
Interincisal angle	131⁰	121⁰	119⁰
Y axis	66⁰	61⁰	62⁰
Upper lip to S line	0mm	2mm	0mm
Lower lip to S line	0mm	-1mm	0mm
Nasolabial angle	90⁰-110⁰	106⁰	105⁰
Inter-canine width		U- 29mm L- 23mm	U- 29mm L- 23mm
Inter-molar width		U- 38mm L- 36mm	U- 38mm L- 36mm

Table 3 Comprehensive cephalometric evaluation

Treatment outcome

Patient was given fixed twin block for 9 months ([Figure 30] ), and simultaneously fixed mechanotherapy was started but there were no positive results obtained after completion of myofunctional therapy due to increased saddle angle. ([Figure 31], [Figure 32], [Figure 33]).

Discussion

Management of class II malocclusion has wide spectrum of options. Growth modulation is often the best option for growing patients. Functional appliances can be used to achieve this goal, and they can be very effective in producing the desired outcome.

The twin block functional appliance has several well-documented advantages over other functional appliances. It is better tolerated by patients, ^[5] more durable, easier to repair, and can be used in both permanent and mixed dentition. Additionally, patients can function normally while wearing the twin block, which makes it easier to wear full-time.

Dr. William J. Clark has stated that patients must be actively growing in order to achieve favorable skeletal changes during treatment. Treatment that coincides with the pubertal growth spurt may produce a more rapid skeletal response. ^[6]

Baccetti et al. found that the best time to start Twin-block therapy for Class II malocclusion is during or slightly after the onset of the pubertal growth spurt.^[7]

To achieve a successful outcome, it is important to choose the right treatment approach for each patient. Not every growing patient with a Class II skeletal base is a good candidate for functional appliance therapy. In addition to do the clinical examination, it is essential to perform a cephalometric evaluation to assess the patient's individual needs before deciding whether to use functional appliances.

Saddle angle emerges as a crucial cephalometric parameter that warrants careful consideration prior to embarking on myofunctional treatment.

Characterized by a sharp drop in early infancy, the saddle angle exhibits a subsequent slowdown in its descent, finally reaching a plateau a few years after puberty. This initial rapid decline, averaging around 5 degrees within the first two years, occurs irrespective of Class I or Class II occlusion. Notably, individual variations in the angle's progression become less pronounced as one matures, with a strong tendency towards stability post-puberty. ^[8]

In a study done by Al Maaitah et al stated that, saddle angle was found to be larger in Class II skeletal relationship as compared to Class I and Class III skeletal relation. ^[9]

Increased   saddle   angle    is present in the cases with posteriorly positioned glenoid fossa and decreased saddle angle is present in cases with anteriorly positioned glenoid fossa. In orthognathic profiles, this deviation in the position of glenoid fossa is compensated by the length of ramus and if not, results in either prognathic or retrognathic profile. Cases with large saddle angle are difficult to treat with functional appliance. ^[4]

In the present study, all the factors are in favour of myofunctional therapy except the saddle angle that was increased.

Following successful completion of the 9-month Phase 1 functional therapy, we achieved all our treatment goals in our first case. Notably, the twin block treatment led to an increase in mandibular unit length, subsequently reflected in a rise in the SNB angle, consistent with C.M. Mills' findings in his study. ^[10] However, after just 2 months of fixed mechanotherapy, relapse occurred. The remaining two cases exhibited no response to the initial myofunctional phase. In all three cases, an elevated saddle angle emerged as the culprit behind treatment relapse, indicating significant mandibular retropositioning relative to the cranial base prior to treatment initiation.

The effectiveness of myofunctional therapy is contingent upon a multitude of factors, rather than a single determinant. This study has demonstrated the substantial influence of saddle angle on achieving successful outcomes in myofunctional treatment.

Conclusion

Functional appliances are widely used in growing patients to achieve the best possible outcomes. However, it is important to remember that every patient is unique, and the effectiveness of treatment can vary depending on a number of factors, most notably the saddle angle.

The saddle angle is a critical determinant of success in functional appliance therapy. Saddle angles between 123° ± 5° are most conducive to successful treatment outcomes. Cases with large saddle angles are less likely to respond to treatment or may relapse.

Meticulous patient selection and personalized treatment planning are essential not only for achieving successful results in myofunctional treatment, but also prevents unnecessary discomfort to the patient and avoiding the wastage of their time on unnecessary treatments.

Source of Funding

None.

Conflict of interest

None.